iec tr 62368-2 · 2021. 7. 15. · 108/757/dc for iec use only 2021-07-16 international...
TRANSCRIPT
108/757/DC For IEC use only
2021-07-16 INTERNATIONAL ELECTROTECHNICAL COMMISSION TECHNICAL COMMITTEE NO. 108: SAFETY OF ELECTRONIC EQUIPMENT WITHIN THE FIELD OF AUDIO/VIDEO, INFORMATION TECHNOLOGY AND COMMUNICATION TECHNOLOGY TC 108/WG HBSDT proposed draft IEC 62368-2, Ed. 4.
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Comments / proposals should be submitted using the IEC Electronic voting system by the National Committees. (See AC/3/2011).
Comments/ proposals to be returned by 2021-09-24
– 2 – 108/757/DC
CONTENTS 1
0 Principles of this product safety standard ...................................................................... 14 2
0.5.1 General ......................................................................................................... 14 3
0.5.7 Equipment safeguards during skilled person service conditions ..................... 16 4
0.10 Thermally-caused injury (skin burn) ............................................................... 16 5
1 Scope ................................................................................................................................ 16 6
2 Normative references ......................................................................................................... 17 7
3 Terms, definitions and abbreviations .................................................................................. 17 8
4 General requirements ........................................................................................................ 20 9
4.1.1 Application of requirements and acceptance of materials, components 10 and subassemblies ........................................................................................ 21 11
4.1.5 Constructions and components not specifically covered ................................. 22 12
4.1.6 Orientation during transport and use .............................................................. 22 13
4.1.8 Liquids and liquid filled components (LFC) ............................................................ 22 14
4.2 Energy source classifications ................................................................................ 22 15
4.2.1 Class 1 energy source ................................................................................... 22 16
4.2.2 Class 2 energy source ................................................................................... 23 17
4.2.3 Class 3 energy source ................................................................................... 23 18
4.3.2 Safeguards for protection of an ordinary person ............................................ 23 19
4.3.3 Safeguards for protection of an instructed person .......................................... 24 20
4.3.4 Safeguards for protection of a skilled person ................................................. 24 21
4.4.2 Composition of a safeguard ........................................................................... 25 22
4.4.3 Safeguard robustness .................................................................................... 25 23
4.6 Fixing of conductors .............................................................................................. 26 24
4.7 Equipment for direct insertion into mains socket-outlets ........................................ 27 25
4.8 Equipment containing coin / button cell batteries ................................................... 27 26
4.9 Likelihood of fire or shock due to entry of conductive objects ................................ 27 27
4.10.3 Power supply cords .............................................................................................. 27 28
5 Electrically-caused injury ................................................................................................... 27 29
5.2.1 Electrical energy source classifications .......................................................... 29 30
5.3.2 Accessibility to electrical energy sources and safeguards .............................. 37 31
5.4 Insulation materials and requirements ................................................................... 38 32
5.4.2 Clearances .................................................................................................... 41 33
5.4.3 Creepage distances ....................................................................................... 53 34
5.4.4 Solid insulation .............................................................................................. 54 35
5.4.5 Antenna terminal insulation............................................................................ 57 36
5.4.6 Insulation of internal wire as a part of a supplementary safeguard ................. 57 37
5.4.7 Tests for semiconductor components and for cemented joints ....................... 58 38
5.4.8 Humidity conditioning .................................................................................... 58 39
5.4.9 Electric strength test ...................................................................................... 58 40
5.4.10 Safeguards against transient voltages from external circuits .......................... 59 41
5.4.11 Separation between external circuits and earth .............................................. 62 42
5.5 Components as safeguards ................................................................................... 62 43
5.5.6 Resistors ....................................................................................................... 65 44
5.5.7 SPDs ............................................................................................................. 65 45
5.5.8 Insulation between the mains and an external circuit consisting of a 46 coaxial cable ................................................................................................. 65 47
– 3 – 108/757/DC
5.6 Protective conductor ............................................................................................. 66 48
5.6.1 General ......................................................................................................... 66 49
5.6.3 Requirements for protective earthing conductors ........................................... 67 50
5.6.4 Requirements for protective bonding conductors ........................................... 67 51
5.6.5 Terminals for protective conductors ............................................................... 67 52
5.6.7 Reliable connection of a protective earthing conductor .................................. 67 53
5.7 Prospective touch voltage, touch current and protective conductor current............ 67 54
5.7.3 Equipment set-up, supply connections and earth connections ........................ 68 55
5.7.5 Earthed accessible conductive parts .............................................................. 68 56
5.7.6 Requirements when touch current exceeds ES2 limits ................................... 68 57
5.7.7 Prospective touch voltage and touch current associated with external 58 circuits ........................................................................................................... 69 59
5.7.8 Summation of touch currents from external circuits ........................................ 70 60
5.8 Backfeed safeguard in battery backed up supplies ................................................ 72 61
6 Electrically-caused fire ...................................................................................................... 74 62
6.2 Classification of power sources (PS) and potential ignition sources (PIS) ............. 74 63
6.2.2 Power source circuit classifications ............................................................... 74 64
6.2.3 Classification of potential ignition sources ..................................................... 77 65
6.3 Safeguards against fire under normal operating conditions and abnormal 66 operating conditions .............................................................................................. 78 67
6.3.1 Requirements ................................................................................................ 81 68
6.3.2 Compliance criteria ........................................................................................ 82 69
6.4 Safeguards against fire under single fault conditions............................................. 83 70
6.4.1 General ......................................................................................................... 83 71
6.4.2 Reduction of the likelihood of ignition under single fault conditions in 72 PS1 circuits ................................................................................................... 90 73
6.4.3 Reduction of the likelihood of ignition under single fault conditions in 74 PS2 circuits and PS3 circuits ......................................................................... 90 75
6.4.4 Control of fire spread in PS1 circuits .............................................................. 92 76
6.4.5 Control of fire spread in PS2 circuits .............................................................. 94 77
6.4.6 Control of fire spread in a PS3 circuit ............................................................ 96 78
6.4.7 Separation of combustible materials from a PIS ............................................. 97 79
6.4.8 Fire enclosures and fire barriers .................................................................... 99 80
6.5.1 General requirements .................................................................................. 105 81
6.5.2 Requirements for interconnection to building wiring ..................................... 106 82
6.6 Safeguards against fire due to the connection of additional equipment................ 106 83
7 Injury caused by hazardous substances ........................................................................... 107 84
8 Mechanically-caused injury .............................................................................................. 110 85
8.1 General ............................................................................................................... 110 86
8.2 Mechanical energy source classifications ............................................................ 110 87
8.2.1 General classification .................................................................................. 110 88
8.2.2 MS1 ............................................................................................................. 111 89
8.2.3 MS2 ............................................................................................................. 111 90
8.2.4 MS3 ............................................................................................................. 111 91
8.3 Safeguards against mechanical energy sources .................................................. 111 92
8.4 Safeguards against parts with sharp edges and corners ..................................... 112 93
8.5 Safeguards against moving parts ........................................................................ 112 94
8.5.1 Requirements .............................................................................................. 112 95
8.6 Stability of equipment ......................................................................................... 113 96
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8.6.3 Relocation stability ...................................................................................... 113 97
8.6.4 Glass slide test ............................................................................................ 113 98
8.6.5 Horizontal force test and compliance criteria................................................ 114 99
8.7 Equipment mounted to a wall, ceiling or other structure ...................................... 114 100
8.7.2 Test methods ............................................................................................... 114 101
8.8 Handle strength .................................................................................................. 115 102
8.8.2 Test method ................................................................................................ 115 103
8.9 Wheels or casters attachment requirements ........................................................ 115 104
8.10 Carts, stands, and similar carriers ....................................................................... 115 105
8.10.1 General ....................................................................................................... 115 106
8.10.2 Marking and instructions .............................................................................. 115 107
8.10.3 Cart, stand or carrier loading test and compliance criteria ............................ 116 108
8.10.4 Cart, stand or carrier impact test.................................................................. 116 109
8.10.5 Mechanical stability ..................................................................................... 116 110
8.10.6 Thermoplastic temperature stability ............................................................. 116 111
8.11 Mounting means for slide-rail mounted equipment (SRME) ................................. 116 112
8.11.1 General ....................................................................................................... 116 113
8.11.3 Mechanical strength test .............................................................................. 117 114
9 Thermal burn injury .......................................................................................................... 117 115
9.1 General ............................................................................................................... 117 116
9.2 Thermal energy source classifications ................................................................. 121 117
9.2.1 TS1 ............................................................................................................. 121 118
9.2.2 TS2 ............................................................................................................. 121 119
9.2.3 TS3 ............................................................................................................. 121 120
9.3 Touch temperature limits ..................................................................................... 122 121
9.3.1 Touch temperature limit requirements .......................................................... 125 122
9.3.2 Test method and compliance criteria ........................................................... 125 123
9.4 Safeguards against thermal energy sources ........................................................ 126 124
9.5.1 Equipment safeguard ................................................................................... 126 125
9.5.2 Instructional safeguard ................................................................................ 126 126
9.6 Requirements for wireless power transmitters ..................................................... 127 127
9.6.3 Test method and compliance criteria ........................................................... 127 128
10 Radiation ....................................................................................................................... 128 129
10.2 Radiation energy source classifications .............................................................. 128 130
10.2.1 General classification .................................................................................. 128 131
10.2.2 & 10.2.3 RS1 and RS2 ...................................................................................... 129 132
10.2.4 RS3 ............................................................................................................. 129 133
10.3 Safeguards against laser radiation ...................................................................... 130 134
10.4 Safeguards against optical radiation from lamps and lamp systems 135 (including LED types) .......................................................................................... 130 136
10.4.1 General Requirements ................................................................................. 130 137
10.5 Safeguards against X-radiation ........................................................................... 130 138
10.6 Safeguards against acoustic energy sources ...................................................... 130 139
10.6.3 Requirements for dose-based systems ........................................................ 131 140
Annex A Examples of equipment within the scope of this standard ............................ 134 141
Annex B Normal operating condition tests, abnormal operating condition tests 142 and single fault condition tests..................................................................................... 134 143
B.1.5 Temperature measurement conditions ......................................................... 135 144
B.1.6 Specific output conditions ............................................................................ 136 145
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B.2.3 Supply Voltage ............................................................................................ 136 146
B.2 – B.3 – B.4 Operating modes....................................................................... 137 147
B.4.4 Functional insulation .................................................................................... 137 148
B.4.8 Compliance criteria during and after single fault conditions .......................... 138 149
Annex C UV Radiation ............................................................................................... 138 150
C.1.1 General ....................................................................................................... 138 151
Annex D Test generators ........................................................................................... 138 152
Annex E Test conditions for equipment containing audio amplifiers ........................... 138 153
Annex F Equipment markings, instructions, and instructional safeguards ................... 139 154
F.3 Equipment markings .......................................................................................... 139 155
F.4 Instructions ......................................................................................................... 139 156
F.5 Instructional safeguards ...................................................................................... 139 157
Annex G Components ................................................................................................ 140 158
G.1 Switches ............................................................................................................. 140 159
G.2.1 Requirements .............................................................................................. 140 160
G.3.3 PTC thermistors ........................................................................................... 140 161
G.3.4 Overcurrent protective devices .................................................................... 141 162
G.3.5 Safeguard components not mentioned in G.3.1 to G.3.4 .............................. 141 163
G.5.1 Wire insulation in wound components .......................................................... 142 164
G.5.2 Endurance test ............................................................................................ 142 165
G.5.3 Transformers ............................................................................................... 142 166
G.5.4 Motors ......................................................................................................... 143 167
G.7 Mains supply cords ............................................................................................ 143 168
G.7.3 – G.7.5 Mains supply cord anchorage, cord entry, bend protection ........ 144 169
G.8 Varistors ............................................................................................................ 144 170
G.9 Integrated circuit (IC) current limiters ................................................................. 144 171
G.11 Capacitors and RC units ..................................................................................... 146 172
G.13 Printed boards .................................................................................................... 146 173
G.13.6 Tests on coated printed boards .................................................................... 146 174
G.14 Coatings on component terminals ....................................................................... 146 175
G.15 Pressurized liquid filled components ................................................................... 146 176
G.15.2 Test methods and compliance criteria for self-contained LFC ...................... 149 177
G.15.3 Test methods and compliance criteria for a Modular LFC ............................. 150 178
Annex H Criteria for telephone ringing signals ........................................................... 153 179
H.2 Method A ........................................................................................................... 153 180
H.3 Method B ........................................................................................................... 155 181
Annex J Insulated winding wires for use without interleaved insulation ...................... 155 182
Annex K Safety interlocks .......................................................................................... 155 183
K.7.1 Safety interlocks ................................................................................................. 155 184
Annex L Disconnect devices ...................................................................................... 156 185
Annex M Equipment containing batteries and their protection circuits ......................... 157 186
M.1 General requirements ......................................................................................... 157 187
M.2 Safety of batteries and their cells ........................................................................ 157 188
M.3 Protection circuits for batteries provided within the equipment ............................ 165 189
M.4 Additional safeguards for equipment containing a portable secondary lithium 190 battery ................................................................................................................ 165 191
M.4.3 Fire enclosure.............................................................................................. 166 192
M.4.4 Drop test of equipment containing a secondary lithium battery ..................... 166 193
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M.6.1 Requirements .............................................................................................. 167 194
M.7.1 Ventilation preventing an explosive gas concentration ................................. 167 195
M.7.2 Test method and compliance criteria ........................................................... 167 196
M.8.2.1 General ....................................................................................................... 167 197
Annex O Measurement of creepage distances and clearances ................................... 168 198
Annex P Safeguards against conductive objects ........................................................ 168 199
P.1 General ............................................................................................................... 168 200
P.2 Safeguards against entry or consequences of entry of a foreign object ............... 168 201
P.3 Safeguards against spillage of internal liquids..................................................... 169 202
P.4 Metalized coatings and adhesives securing parts ................................................ 169 203
Annex Q Circuits intended for interconnection with building wiring ............................. 169 204
Q.1.1 Requirements .............................................................................................. 169 205
Q.1.2 Test method and compliance criteria ........................................................... 169 206
Q.2 Test for external circuits – paired conductor cable ............................................. 170 207
Annex R Limited short-circuit test .............................................................................. 170 208
Annex S Tests for resistance to heat and fire ............................................................. 170 209
S.1 Flammability test for fire enclosure and fire barrier materials of equipment 210 where the steady-state power does not exceed 4 000 W ..................................... 170 211
S.2 Flammability test for fire enclosure and fire barrier integrity ............................... 170 212
S.3 Flammability tests for the bottom of a fire enclosure ........................................... 171 213
S.4 Flammability classification of materials ............................................................... 171 214
S.5 Flammability test for fire enclosure materials of equipment with a steady 215 state power exceeding 4 000 W .......................................................................... 171 216
Annex T Mechanical strength tests ............................................................................ 172 217
T.2 Steady force test, 10 N ....................................................................................... 172 218
T.3 Steady force test, 30 N ....................................................................................... 172 219
T.4 Steady force test, 100 N ..................................................................................... 172 220
T.5 Steady force test, 250 N ..................................................................................... 172 221
T.6 Enclosure impact test .......................................................................................... 172 222
T.7 Drop test ............................................................................................................. 172 223
T.8 Stress relief test .................................................................................................. 172 224
T.9 Glass impact test ............................................................................................... 172 225
T.10 Glass fragmentation test ..................................................................................... 173 226
Annex U Mechanical strength of CRTs and protection against the effects of 227 implosion 173 228
U.2 Test method and compliance criteria for non-intrinsically protected CRTs ........... 173 229
Annex V Determination of accessible parts ................................................................ 173 230
Figure V.3 Blunt probe ............................................................................... 173 231
Annex X Alternative method for determining clearances for insulation in circuits 232 connected to an AC mains not exceeding 420 V peak (300 V RMS) ............................. 173 233
Annex Y Construction requirements for outdoor enclosures ....................................... 174 234
Y.3 Resistance to corrosion ...................................................................................... 176 235
Y.4.6 Securing means .................................................................................................. 176 236
237
Figure 1 – Risk reduction as given in ISO/IEC Guide 51........................................................ 15 238
Figure 2 – HBSE Process Chart ............................................................................................ 16 239
Figure 3 – Protective bonding conductor as part of a safeguard ............................................ 19 240
Figure 4 – Safeguards for protecting an ordinary person ....................................................... 23 241
– 7 – 108/757/DC Figure 5 – Safeguards for protecting an instructed person .................................................... 24 242
Figure 6 – Safeguards for protecting a skilled person ............................................................ 24 243
Figure 7 – Flow chart showing the intent of the glass requirements ....................................... 26 244
Figure 8 – Conventional time/current zones of effects of AC currents (15 Hz to 100 Hz) 245 on persons for a current path corresponding to left hand to feet (see IEC TS 60479-246 1:2005, Figure 20) ................................................................................................................ 29 247
Figure 9 – Conventional time/current zones of effects of DC currents on persons for a 248 longitudinal upward current path (see IEC TS 60479-1:2005, Figure 22) ............................... 30 249
Figure 10 – Illustration that limits depend on both voltage and current .................................. 31 250
Figure 11 – Illustration of working voltage ............................................................................. 43 251
Figure 12 – Illustration of transient voltages on paired conductor external circuits ................ 45 252
Figure 13 – Illustration of transient voltages on coaxial-cable external circuits ...................... 46 253
Figure 14 – Basic and reinforced insulation in Table 14 of IEC 62368-1:2018; ratio 254 reinforced to basic ................................................................................................................ 48 255
Figure 15 – Reinforced clearances according to Rule 1, Rule 2, and Table 14 ...................... 50 256
Figure 16 – Example illustrating accessible internal wiring .................................................... 58 257
Figure 17 – Waveform on insulation without surge suppressors and no breakdown ............... 60 258
Figure 18 – Waveforms on insulation during breakdown without surge suppressors .............. 61 259
Figure 19 – Waveforms on insulation with surge suppressors in operation ............................ 61 260
Figure 20 – Waveform on short-circuited surge suppressor and insulation ............................ 61 261
Figure 21 – Example for an ES2 source ................................................................................ 63 262
Figure 22 – Example for an ES3 source ................................................................................ 63 263
Figure 23 – Overview of protective conductors ...................................................................... 66 264
Figure 24 – Example of a typical touch current measuring network ....................................... 68 265
Figure 25 – Touch current from a floating circuit ................................................................... 70 266
Figure 26 – Touch current from an earthed circuit ................................................................. 71 267
Figure 27 – Summation of touch currents in a PABX ............................................................. 71 268
Figure 28 – Possible safeguards against electrically-caused fire ........................................... 78 269
Figure 29 – Fire clause flow chart ......................................................................................... 81 270
Figure 30 – Prevent ignition flow chart .................................................................................. 86 271
Figure 31 – Control fire spread summary .............................................................................. 87 272
Figure 32 – Control fire spread PS2 ...................................................................................... 88 273
Figure 33 – Control fire spread PS3 ...................................................................................... 89 274
Figure 34 – Fire cone application to a large component ........................................................ 98 275
Figure 35 – Flowchart demonstrating the hierarchy of hazard management ........................ 109 276
Figure 36 – Model for chemical injury .................................................................................. 110 277
Figure 37 – Direction of forces to be applied ....................................................................... 114 278
Figure 38 – Model for a burn injury ..................................................................................... 118 279
Figure 39 – Model for safeguards against thermal burn injury ............................................. 120 280
Figure 40 – Model for absence of a thermal hazard ............................................................. 120 281
Figure 41 – Model for presence of a thermal hazard with a physical safeguard in place ...... 120 282
Figure 42 – Model for presence of a thermal hazard with behavioural safeguard in 283 place................................................................................................................................... 121 284
Figure 45 – Examples of symmetrical single coils ............................................................... 127 285
Figure 45 – Flowchart for evaluation of Image projectors (beamers) ................................... 129 286
– 8 – 108/757/DC Figure 46 – Graphical representation of LAeq,T .................................................................. 131 287
Figure 47 – Overview of operating modes ........................................................................... 137 288
Figure 48 – Voltage-current characteristics (Typical data) ................................................... 141 289
Figure 49 – Example of IC current limiter circuit .................................................................. 145 290
Figure 51 – Decision flowchart ............................................................................................ 147 291
Figure 52 – Illustration of a self-contained LFC system ....................................................... 149 292
Figure 53 – Illustration of a modular LFC system ................................................................ 150 293
Figure 54 – Example illustration of a rack modular LFC subsystems with internal and 294 external connections. .......................................................................................................... 151 295
Figure 55 – CDU Liquid Cooling System within a Data Center (courtesy of ASHRAE 296 TC9.9) ................................................................................................................................ 152 297
Figure 50 – Current limit curves .......................................................................................... 154 298
Figure 51 – Example of a dummy battery circuit .................................................................. 166 299
Figure 52 – Example of a circuit with two power sources..................................................... 170 300
Figure A.1 – Installation has poor earthing and bonding; equipment damaged 301 (from ITU-T K.66) ................................................................................................................ 178 302
Figure A.2 – Installation has poor earthing and bonding; using main earth bar for 303 protection against lightning strike (from ITU-T K.66) ........................................................... 178 304
Figure A.3 – Installation with poor earthing and bonding, using a varistor ........................... 179 305
Figure A.4 – Typîcal example of a surge suppressor and a voltage fall ............................... 179 306
Figure A.5 – An example of surge voltage drop by a MOV and two GDTs (measured in 307 laboratory) .......................................................................................................................... 181 308
Figure A.6 – An example of ports of telecommunication equipment ..................................... 185 309
Figure A.7 – V-I properties of gas discharge tubes .............................................................. 186 310
Figure A.7 – Holdover ......................................................................................................... 187 311
Figure A.9 – Relation of the V-I characteristic of a gas discharge tube and the output 312 characteristic of the power supply ....................................................................................... 188 313
Figure A.10 – Characteristics .............................................................................................. 189 314
Figure A.11 – Follow on current pictures ............................................................................. 190 315
Figure B.1 – Typical EMC filter schematic ........................................................................... 191 316
Figure B.2 – 100 MΩ oscilloscope probes ........................................................................... 193 317
Figure B.3 – Combinations of EUT resistance and capacitance for 1 s time constant .......... 195 318
Figure B.4 – 240 V mains followed by capacitor discharge .................................................. 197 319
Figure B.5 – Time constant measurement schematic .......................................................... 198 320
Figure B.6 – Worst-case measured time constant values for 100 MΩ and 10 MΩ probes .... 202 321
Figure D.1 – Example of circuit configuration of a surge suppresser ................................... 204 322
323
Table 1 – General summary of required safeguards .............................................................. 24 324
Table 2 – Time/current zones for AC 15 Hz to 100 Hz for hand to feet pathway (see 325 IEC TS 60479-1:2005, Table 11) ........................................................................................... 30 326
Table 3 – Time/current zones for DC for hand to feet pathway (see IEC TS 60479-327 1:2005, Table 13).................................................................................................................. 31 328
Table 4 – Limit values of accessible capacitance (threshold of pain) ..................................... 34 329
Table 5 – Total body resistances RT for a current path hand to hand, DC, for large 330
surface areas of contact in dry condition ............................................................................... 36 331
– 9 – 108/757/DC Table 6 – Insulation requirements for external circuits .......................................................... 46 332
Table 7 – Voltage drop across clearance and solid insulation in series ................................. 52 333
Table 8 – Examples of application of various safeguards ...................................................... 80 334
Table 9 – Basic safeguards against fire under normal operating conditions and 335 abnormal operating conditions .............................................................................................. 82 336
Table 10 – Supplementary safeguards against fire under single fault conditions ................... 83 337
Table 11 – Method 1: Reduce the likelihood of ignition ......................................................... 85 338
Table 12 – Method 2: Control fire spread .............................................................................. 93 339
Table 13 – Fire barrier and fire enclosure flammability requirements ................................... 100 340
Table 14 – Summary – Fire enclosure and fire barrier material requirements ...................... 104 341
Table 15 – Control of chemical hazards .............................................................................. 108 342
Table 16 – Overview of requirements for dose-based systems ............................................ 133 343
Table 17 – Overview of supply voltage ................................................................................ 136 344
Table 17 – Safety of batteries and their cells – requirements (expanded information on 345 documents and scope) ........................................................................................................ 159 346
Table A.1 – Permissible power-frequency stress voltage (except for US and Japan) ........... 181 347
Table A.2 – TOV parameters for US systems quoted from IEC 61643-12:2020 ................... 182 348
Table A.3 – TOV test parameters for Japanese systems quoted from IEC 61643-349 12:2020 .............................................................................................................................. 182 350
Table A.4 – Peak voltage of TOV in countries conforming IEC 60364-4-44 ......................... 183 351
Table A.5 – Peak voltage of TOV in US............................................................................... 183 352
Table A.6 – Peak voltage of TOV in Japan .......................................................................... 183 353
Table A.7 – The value of Upeak2 for major mains voltages ................................................. 184 354
Table B.1 – 100 MΩ oscilloscope probes ............................................................................ 193 355
Table B.2 – Capacitor discharge ......................................................................................... 194 356
Table B.3 – Maximum Tmeasured values for combinations of REUT and CEUT for 357
TEUT of 1 s ........................................................................................................................ 201 358
359
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INTERNATIONAL ELECTROTECHNICAL COMMISSION 361
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363
AUDIO/VIDEO, INFORMATION AND 364
COMMUNICATION TECHNOLOGY EQUIPMENT – 365
366
Part 2: Explanatory information related to IEC 62368-1:202x 367
368
FOREWORD 369
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising 370 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international 371 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and 372 in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, 373 Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their 374 preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with 375 may participate in this preparatory work. International, governmental and non-governmental organizations liaising 376 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for 377 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 378
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international 379 consensus of opinion on the relevant subjects since each technical committee has representation from all 380 interested IEC National Committees. 381
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National 382 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC 383 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any 384 misinterpretation by any end user. 385
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications 386 transparently to the maximum extent possible in their national and regional publications. Any divergence between 387 any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 388
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity 389 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any 390 services carried out by independent certification bodies. 391
6) All users should ensure that they have the latest edition of this publication. 392
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and 393 members of its technical committees and IEC National Committees for any personal injury, property damage or 394 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and 395 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 396
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is 397 indispensable for the correct application of this publication. 398
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent 399 rights. IEC shall not be held responsible for identifying any or all such patent rights. 400
The main task of IEC technical committees is to prepare International Standards. However, a 401 technical committee may propose the publication of a technical report when it has collected 402 data of a different kind from that which is normally published as an International Standard, for 403 example, "state of the art". 404
IEC 62368-2, which is a Technical Report, has been prepared by IEC technical committee 405 TC 108: Safety of electronic equipment within the field of audio/video, information technology 406 and communication technology. 407
This fourth edition updates the third edition of IEC 62368-2 published in 2018 to take into 408 account changes made to IEC 62368-1:202x as identified in the Foreword of IEC 62368-1:202x. 409
This Technical Report is informative only. In case of a conflict between IEC 62368-1 and IEC 410 TR 62368-2, the requirements in IEC 62368-1 prevail over this Technical Report. 411
– 11 – 108/757/DC The text of this technical report is based on the following documents: 412
Enquiry draft Report on voting
108/xyz/DTR 108/xyz/RVDTR
413 Full information on the voting for the approval of this technical report can be found in the report 414 on voting indicated in the above table. 415
In this document, the following print types are used: 416
– notes/explanatory matter: in smaller roman type; 417
– tables and figures that are included in the rationale have linked fields (shaded in grey if 418 “field shading” is active); 419
– terms that are defined in IEC 62368-1: in bold type. 420
In this document, where the term (HBSDT) is used, it stands for Hazard Based Standard 421 Development Team, which is the Working Group of IEC TC 108 responsible for the development 422 and maintenance of IEC 62368-1. 423
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. 424
A list of all parts of the IEC 62368 series can be found, under the general title Audio/video, 425 information and communication technology equipment, on the IEC website. 426
In this document, only those subclauses from IEC 62368-1 considered to need further 427 background reference information or explanation to benefit the reader in applying the relevant 428 requirements are included. Therefore, not all numbered subclauses are cited. Unless otherwise 429 noted, all references are to clauses, subclauses, annexes, figures or tables located in 430 IEC 62368-1:202x. 431
The entries in the document may have one or two of the following subheadings in addition to 432 the Rationale statement: 433
Source – where the source is known and is a document that is accessible to the general public, 434 a reference is provided. 435
Purpose – where there is a need and when it may prove helpful to the understanding of the 436 Rationale, we have added a Purpose statement. 437
438
– 12 – 108/757/DC The committee has decided that the contents of this publication will remain unchanged until the 439 stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to 440 the specific publication. At this date, the publication will be 441
• reconfirmed, 442
• withdrawn, 443
• replaced by a revised edition, or 444
• amended. 445
446
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents. Users should therefore print this document using a colour printer.
447
448
– 13 – 108/757/DC
INTRODUCTION 449
IEC 62368-1 is based on the principles of hazard-based safety engineering, which is a different 450 way of developing and specifying safety considerations than that of the current practice. While 451 this document is different from traditional IEC safety documents in its approach and while it is 452 believed that IEC 62368-1 provides a number of advantages, its introduction and evolution are 453 not intended to result in significant changes to the existing safety philosophy that led to the 454 development of the safety requirements contained in IEC 60065 and IEC 60950-1. The 455 predominant reason behind the creation of IEC 62368-1 is to simplify the problems created by 456 the merging of the technologies of ITE and CE. The techniques used are novel, so a learning 457 process is required and experience is needed in its application. Consequently, the committee 458 recommends that this edition of the document be considered as an alternative to IEC 60065 or 459 IEC 60950-1 at least over the recommended transition period. 460
461
462
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AUDIO/VIDEO, INFORMATION AND 463
COMMUNICATION TECHNOLOGY EQUIPMENT – 464
465
Part 2: Explanatory information related to IEC 62368-1:202x 466
467
468
0 Principles of this product safety standard 469
Clause 0 is informational and provides a rationale for the normative clauses 470 of the document. 471
0.5.1 General 472
ISO/IEC Guide 51:2014, 6.3.5 states: 473
“When reducing risks, the order of priority shall be as follows: 474
a) inherently safe design; 475
b) guards and protective devices; 476
c) information for end users. 477
Inherently safe design measures are the first and most important step in the 478 risk reduction process. This is because protective measures inherent to the 479 characteristics of the product or system are likely to remain effective, 480 whereas experience has shown that even well-designed guards and 481 protective devices can fail or be violated and information for use might not 482 be followed. 483
Guards and protective devices shall be used whenever an inherently safe 484 design measure does not reasonably make it possible either to remove 485 hazards or to sufficiently reduce risks. Complementary protective measures 486 involving additional equipment (for example, emergency stop equipment) 487 might have to be implemented. 488
The end user has a role to play in the risk reduction procedure by complying 489 with the information provided by the designer/supplier. However, information 490 for use shall not be a substitute for the correct application of inherently safe 491 design measures, guards or complementary protective measures.” 492
In general, this principle is used in IEC 62368-1. The table below shows a 493 comparison between the hierarchy required in ISO/IEC Guide 51 and the 494 hierarchy used in IEC 62368-1: 495
ISO/IEC Guide 51 IEC 62368-1 a) inherently safe design 1. inherently safe design by limiting all energy
hazards to class 1 b) guards and protective devices 2. equipment safeguards
3. installation safeguards 4. personal safeguards
c) information for end users 5. behavioral safeguards 6. instructional safeguards
496
Risk assessment has been considered as part of the development of 497 IEC 62368-1 as indicated in the following from ISO/IEC Guide 51 (Figure 1) 498 in this document. See also the Hazard Based Safety Engineering (HBSE) 499 Process Flow (Figure 2) in this document that also provides additional details 500 for the above comparison. 501
– 15 – 108/757/DC
502
Figure 1 – Risk reduction as given in ISO/IEC Guide 51 503
– 16 – 108/757/DC
504
505
Figure 2 – HBSE Process Chart 506
0.5.7 Equipment safeguards during skilled person service conditions 507
Purpose: To explain the intent of requirements for providing safeguards against 508 involuntary reaction. 509
Rationale: By definition, a skilled person has the education and experience to identify all 510 class 3 energy sources to which he may be exposed. However, while servicing 511 one class 3 energy source in one location, a skilled person may be exposed to 512 another class 3 energy source in a different location. 513
In such a situation, either of two events is possible. First, something may cause 514 an involuntary reaction of the skilled person with the consequences of contact 515 with the class 3 energy source in the different location. Second, the space in 516 which the skilled person is located may be small and cramped, and inadvertent 517 contact with a class 3 energy source in the different location may be likely. 518
In such situations, this document may require an equipment safeguard solely for 519 the protection of a skilled person while performing servicing activity. 520
0.10 Thermally-caused injury (skin burn) 521
Purpose: The requirements basically address safeguards against thermal energy transfer 522 by conduction. They do not specifically address safeguards against thermal 523 energy transfer by convection or radiation. However, as the temperatures from 524 hot surfaces due to conduction are always higher than the radiated or convected 525 temperatures, these are considered to be covered by the requirements against 526 conducted energy transfer. 527
___________ 528
1 Scope 529
Purpose: To identify the purpose and applicability of this document and the exclusions 530 from the scope. 531
– 17 – 108/757/DC Rationale: The scope excludes requirements for functional safety. Functional safety is 532
addressed in IEC 61508-1. Because the scope includes computers that may 533 control safety systems, functional safety requirements would necessarily include 534 requirements for computer processes and software. 535
The requirements provided in IEC 60950-23 could be modified and added to 536 IEC 62368 as another –X document. However, because of the hazard-based 537 nature of IEC 62368-1, the requirements from IEC 60950-23 have been 538 incorporated into the body of IEC 62368-1 and made more generic. 539
The intent of the addition of the IEC 60950-23 requirements is to maintain the 540 overall intent of the technical requirements from IEC 60950-23, incorporate them 541 into IEC 62368-1 following the overall format of IEC 62368-1 and simplify and 542 facilitate the application of these requirements. 543
Robots traditionally are covered under the scopes of ISO documents, typically 544 maintained by ISO TC 299. ISO TC 299 has working groups for personal care 545 robots and service robots, and produces for example, ISO 13482, Robots and 546 robotic devices – Safety requirements for personal care robots. 547
___________ 548
2 Normative references 549
The list of normative references is a list of all documents that have a normative 550 reference to it in the body of the document. As such, referenced documents are 551 indispensable for the application of this document. For dated references, only 552 the edition cited applies. For undated references, the latest edition of the 553 referenced document (including any amendments) applies. 554
Recently, there were some issues with test houses that wanted to use the latest 555 edition as soon as it was published. As this creates serious problems for 556 manufacturers, since they have no chance to prepare, it was felt that a 557 reasonable transition period should be taken into account. This is in line with 558 earlier decisions taken by the SMB that allow transition periods to be mentioned 559 in the foreword of the documents. Therefore IEC TC 108 decided to indicate this 560 in the introduction of the normative references clause, to instruct test houses to 561 take into account any transition period, effective date or date of withdrawal 562 established for the document. 563
These documents are referenced, in whole, in part, or as alternative 564 requirements to the requirements contained in this document. Their use is 565 specified, where necessary, for the application of the requirements of this 566 document. The fact that a standard is mentioned in the list does not mean that 567 compliance with the document or parts of it are required. 568
___________ 569
3 Terms, definitions and abbreviations 570
Rationale is provided for definitions that deviate from IEV definitions or from 571 Basic or Group Safety publication definitions. 572
3.3.2.1 electrical enclosure 573
Source: IEC 60050-195:1998, 195-06-13 574
Purpose: To support the concept of safeguards as used in this document. 575
– 18 – 108/757/DC Rationale: The IEV definition is modified to use the term “safeguard” in place of the word 576
“protection”. The word “safeguard” identifies a physical “thing” whereas the word 577 “protection” identifies the act of protecting. This document sets forth 578 requirements for use of physical safeguards and requirements for those 579 safeguards. The safeguards provide “protection” against injury from the 580 equipment. 581
3.3.3.2 fixed equipment 582
Source: IEC 60050-826:2004, modified 583
Purpose: To support the concept of “Fixed Equipment” and ensure the stability of certified 584 products. 585
Rationale: The means of securement by the manufacturer must be in accordance with the 586 accepted definition of “fixed equipment” (IEC 60050-826:2004) and reasonably 587 sufficient to overcome the forces of instability. 588
3.3.5.1 basic insulation 589
Source: IEC 60050-195:1998, 195-06-06 590
Purpose: To support the concept of safeguards as used in this document. 591
Rationale: The IEV definition is modified to use the term “safeguard” in place of the word 592 “protection”. The word “safeguard” identifies a physical “thing” whereas the word 593 “protection” identifies the act of protecting. This document sets forth 594 requirements for use of physical safeguards and requirements for those 595 safeguards. The safeguards provide “protection” against injury from the 596 equipment. 597
3.3.5.2 double insulation 598
Source: IEC 60050-195:1998, 195-06-08 599
Purpose: To support the concept of safeguards as used in this document. 600
Rationale: See 3.3.5.1, basic insulation. 601
3.3.5.6 solid insulation 602
Source: IEC 60050-212:2015, 212-11-02 603
3.3.5.7 supplementary insulation 604
Source: IEC 60050-195:1998, 195-06-07 605
Purpose: To support the concept of safeguards as used in this document. 606
Rationale: See 3.3.5.1, basic insulation. 607
3.3.6.9 restricted access area 608
Source: IEC 60050-195:1998, 195-04-04 609
Purpose: To use the concept of “instructed persons” and “skilled persons” as used in 610 this document. 611
Rationale: The IEV definition is modified to use the terms “instructed persons” and 612 “skilled persons” rather than “electrically instructed persons” and “electrically 613 skilled persons.” 614
– 19 – 108/757/DC 3.3.7.7 reasonably foreseeable misuse 615
Source: ISO/IEC Guide 51:2014, 3.7 616
Rationale: Misuse depends on personal objectives, personal perception of the equipment, 617 and the possible use of the equipment (in a manner not intended by the 618 manufacturer) to accomplish those personal objectives. Equipment within the 619 scope of this document ranges from small handheld equipment to large, 620 permanently installed equipment. There is no commonality among the equipment 621 for readily predicting human behaviour leading to misuse of the equipment and 622 resultant injury. Where a possible reasonably foreseeable misuse that may 623 lead to an injury is not covered by the requirements of the document, 624 manufacturers are encouraged to consider reasonably foreseeable misuse of 625 equipment and provide safeguards, as applicable, to prevent injury in the event 626 of such misuse. (Not all reasonably foreseeable misuse of equipment results 627 in injury or potential for injury.) 628
3.3.8.1 instructed person 629
Source: IEC 60050-826:2004, 826-18-02 630
Rationale: The IEV definition is modified to use the terms “energy sources”, “skilled 631 persons”, and “precautionary safeguard”. The definition is made stronger by 632 using the term “instructed” rather than “advised”. 633
3.3.8.3 skilled person 634
Source: IEC 60050-826:2004, 826-18-01 635
Rationale: The IEV definition is modified to use the phrase “to reduce the likelihood of”. 636 IEC 62368-1, in general, tends not use the word “hazard”. 637
3.3.11.9 protective bonding conductor 638
Rationale: The protective bonding conductor, is not a complete safeguard, but a 639 component part of the earthing system safeguard. The protective bonding 640 conductor provides a fault current pathway from a part (insulated from ES3 by 641 basic insulation only) to the equipment protective earthing terminal, see 642 Figure 3 in this document. 643
644
Figure 3 – Protective bonding conductor as part of a safeguard 645
The parts required to be earthed via a protective bonding conductor are those 646 that have only basic insulation between the parts and ES3, and are connected 647 to accessible parts. 648
Only the fault current pathway is required to be a protective bonding 649 conductor. Other earthing connections of accessible conductive parts can be 650 by means of a functional earth conductor to the equipment PE terminal or to a 651 protective bonding conductor. 652
– 20 – 108/757/DC 3.3.14.3 prospective touch voltage 653
Source: IEC 60050-195:1998, 195-05-09 654
Purpose: To properly identify electric shock energy source voltages. 655
Rationale: The IEV definition is modified to delete “animal”. The word “person” is also 656 deleted as all of the requirements in the document are with respect to persons. 657
3.3.14.8 working voltage 658
Source: IEC 60664-1:2020, 3.1.7 659
Purpose: To distinguish between RMS. working voltage and the peak of the working 660 voltage. 661
Rationale: The IEC 60664-1 definition is modified to delete “RMS”. IEC 62368-1 uses both 662 RMS. working voltage and peak of the working voltage; each term is defined. 663
3.3.15.2 class II construction 664
Source: IEC 60335-1:2010, 3.3.11 665
Purpose: Although the term is not used in the document, for completeness, it was decided 666 to retain this definition. 667
Rationale: The word “appliance” is changed to “equipment”. 668
____________ 669
4 General requirements 670
Purpose: To explain how to investigate and determine whether or not safety is involved. 671
Rationale: In order to establish whether or not safety is involved, the circuits and 672 construction are investigated to determine whether the consequences of 673 possible fault conditions would lead to an injury. Safety is involved if, as a result 674 of a single fault condition, the consequences of the fault lead to a risk of injury. 675
If a fault condition should lead to a risk of injury, the part, material, or device 676 whose fault was simulated may comprise a safeguard. 677
Rationale is provided for questions regarding the omission of some traditional 678 requirements appearing in other safety documents. Rationale is also provided 679 for further explanation of new concepts and requirements in this document. 680
Reasonable foreseeable misuse 681
Rationale: Apart from Annex M, this document does not specifically mention foreseeable 682 misuse or abnormal operating conditions. Nevertheless, the requirements of 683 the document cover many kinds of foreseeable misuse, such as covering of 684 ventilation openings, paper jams, stalled motors, etc. 685
functional insulation 686
Rationale: This document does not include requirements for functional insulation. By its 687 nature, functional insulation does not provide a safeguard function against 688 electric shock or electrically-caused fire and therefore may be faulted. Obviously, 689 not all functional insulations are faulted as this would be prohibitively time-690 consuming. Sites for functional insulation faults should be based upon physical 691 examination of the equipment, and upon the electrical schematic. 692
Note that basic insulation and reinforced insulation may also serve as 693 functional insulation, in which case the insulation is not faulted. 694
– 21 – 108/757/DC functional components 695
Rationale: This document does not include requirements for functional components. By 696 their nature, individual functional components do not provide a safeguard 697 function against electric shock, electrically-caused fire, thermal injury, etc., and 698 therefore may be candidates for fault testing. Obviously, not all functional 699 components are faulted as this would be prohibitively time-consuming. 700 Candidate components for fault testing should be based upon physical 701 examination of the equipment, upon the electrical schematic diagrams, and 702 whether a fault of that component might result in conditions for electric shock, 703 conditions for ignition and propagation of fire, conditions for thermal injury, etc. 704
As with all single fault condition testing (Clause B.4), upon faulting of a 705 functional component, there shall not be any safety consequence (for example, 706 a benign consequence), or a basic safeguard, supplementary safeguard , or 707 reinforced safeguard shall remain effective. 708
In some cases, a pair of components may comprise a safeguard. If the fault of 709 one of the components in the pair is mitigated by the second component, then 710 the pair is designated as a double safeguard. For example, if two diodes are 711 employed in series to protect a battery from reverse charge, then the pair 712 comprises a double safeguard and the components should be limited to the 713 manufacturer and part number actually tested. A second example is that of an 714 X-capacitor and discharge resistor. If the discharge resistor should fail open, 715 then the X-capacitor will not be discharged. Therefore, the X-capacitor value is 716 not to exceed the ES2 limits specified for a charged capacitor. Again, the two 717 components comprise a double safeguard and the values of each component 718 are limited to values for ES1 under normal operating conditions and the values 719 for ES2 under single fault conditions. 720
4.1.1 Application of requirements and acceptance of materials, components and 721 subassemblies 722
Purpose: To accept components as safeguards. 723
Rationale: This document includes requirements for safeguard components. A safeguard 724 component is a component specifically designed and manufactured for both 725 functional and safeguard parameters. Examples of safeguard components are 726 capacitors complying with IEC 60384-14 and other components that comply with 727 their related IEC component document. 728
Acceptance of components and component requirements from IEC 60065 729 and 60950-1 730
Purpose: To accept both components and sub-assemblies investigated to the legacy 731 documents, IEC 60065 and IEC 60950-1, and components complying with 732 individual component requirements within these documents during the transition 733 period. 734
Rationale: To facilitate a smooth transition from the legacy documents IEC 60065 and 735 IEC 60950-1 to IEC 62368-1, including by the component supply chain, this 736 document allows for acceptance of both components and sub-assemblies 737 investigated to the legacy documents. Individual component requirements within 738 these documents may be used for compliance with IEC 62368-1 without further 739 investigation, other than to give consideration to the appropriate use of the 740 component or sub-assembly in the end-product. 741
This means, for example, if a switch mode power supply is certified to IEC 60065 742 or IEC 60950-1, this component can be used in equipment evaluated to 743 IEC 62368-1 without further investigation, other than to give consideration to the 744 appropriate use of the component, such as use within its electrical ratings. 745
– 22 – 108/757/DC
This also means, for example, since IEC 60950-1 allows for wiring and cables 746 insulated with PVC, TFE, PTFE, FEP, polychloroprene or polyimide to comply 747 with material requirements for parts within a fire enclosure without need for the 748 application of a flammability test, the same wire can be used to comply with the 749 requirements in 6.5.2 for insulation on wiring used in PS2 or PS3 circuits and 750 without the need for application of a flammability test per IEC 60332 series or 751 IEC TS 60695-11-21 as normally is required by 6.5.1. 752
4.1.5 Constructions and components not specifically covered 753
For constructions not covered, consideration should be given for the hierarchy 754 of safeguards in accordance with ISO/IEC Guide 51. 755
4.1.6 Orientation during transport and use 756
See also 4.1.4 757
In general, equipment is assumed to be installed and used in accordance with 758 the manufacturer’s instructions. However, in some cases where equipment may 759 be installed by an ordinary person, it is recognized that it is common practice 760 to mount equipment as desired if screw holes are provided, especially if they 761 allow mounting to readily available brackets. Hence, the exception that is added 762 to 4.1.6. 763
Examples of the above: a piece of equipment, such as a television set or a video 764 projector, that has embedded screw mounting holes that allow it to be attached 765 to a wall or other surface through the use of commercially available vertically or 766 tilt-mountable brackets, shall also take into account that the mounting surface 767 itself may not be vertical. 768
It is also recognized that transportable equipment, by its nature, may be 769 transported in any and all orientations. 770
4.1.8 Liquids and liquid filled components (LFC) 771
The one-litre (1 l) restriction was placed in 4.1.8 since the origin of some of the 772 requirements in Clause G.15 came from requirements in documents often 773 applied to smaller systems. Nevertheless, such a limitation does not always 774 negate the allowed application of 4.1.8 and Clause G.15 to systems with larger 775 volumes of liquid, but it could impact direct (automatic) applicability to the larger 776 systems. 777
4.2 Energy source classifications 778
Classification of energy sources may be done whether the source is accessible 779 or not. The requirements for parts may differ on whether the part is accessible 780 or not. 781
4.2.1 Class 1 energy source 782
A class 1 energy source is a source that is expected not to create any pain or 783 injury. Therefore, a class 1 energy source may be accessible by any person. 784
Under some specific conditions of abnormal operation or single fault 785 conditions, a class 1 energy source may reach class 2 limits. However, this 786 source still remains a class 1 energy source. In this case, an instructional 787 safeguard may be required. 788
Under normal operating conditions and abnormal operating conditions, the 789 energy in a class 1 source, in contact with a body part, may be detectable, but 790 is not painful nor is it likely to cause an injury. For fire, the energy in a class 1 791 source is not likely to cause ignition. 792
Under single fault conditions, a class 1 energy source, under contact with a 793 body part, may be painful, but is not likely to cause injury. 794
– 23 – 108/757/DC 4.2.2 Class 2 energy source 795
A class 2 energy source is a source that may create pain, but which is unlikely 796 to create any serious injury. Therefore, a class 2 energy source may not be 797 accessible by an ordinary person. However, a class 2 energy source may be 798 accessible by: 799
– an instructed person; and 800
– a skilled person. 801
The energy in a class 2 source, under contact with a body part, may be painful, 802 but is not likely to cause an injury. For fire, the energy in a class 2 source can 803 cause ignition under some conditions. 804
4.2.3 Class 3 energy source 805
A class 3 energy source is a source that is likely to create an injury. Therefore, 806 a class 3 energy source may not be accessible to an ordinary person or an 807 instructed person. A class 3 energy source may, in general, be accessible to 808 a skilled person. 809
Any source may be declared a class 3 energy source without measurement, in 810 which case all the safeguards applicable to class 3 are required. 811
The energy in a class 3 source, under contact with a body part, is capable of 812 causing injury. For fire, the energy in a class 3 source may cause ignition and 813 the spread of flame where fuel is available. 814
4.3.2 Safeguards for protection of an ordinary person 815
The required safeguards for the protection of an ordinary person are given in Figure 4. 816
817
Figure 4 – Safeguards for protecting an ordinary person 818
– 24 – 108/757/DC 4.3.3 Safeguards for protection of an instructed person 819
The required safeguards for the protection of an instructed person are given in Figure 5. 820
821
Figure 5 – Safeguards for protecting an instructed person 822
4.3.4 Safeguards for protection of a skilled person 823
The required safeguards for the protection of a skilled person are given in Figure 6. 824
825
Figure 6 – Safeguards for protecting a skilled person 826
Table 1 in this document gives a general overview of the required number of 827 safeguards depending on the energy source and the person to whom the energy 828 source is accessible. The different clauses have requirements that sometimes 829 deviate from the general principle as given above. These cases are clearly 830 defined in the requirements sections of the document. 831
Table 1 – General summary of required safeguards 832
Person
Number of safeguards required to be interposed between an energy source and a person
Class 1 Class 2 Class3
Ordinary person 0 1 2
Instructed person 0 0 2
Skilled person 0 0 0 or 1
833
– 25 – 108/757/DC For a skilled person, there is normally no safeguard required for a class 3 834
energy source. However, if there are multiple class 3 energy sources accessible 835 or if the energy source is not obvious, a safeguard may be required. 836
4.4.2 Composition of a safeguard 837
Purpose: To specify design and construction criteria for a single safeguard (basic, 838 supplementary, or reinforced) comprised of more than one element, for example, 839 a component or a device. 840
Rationale: Safeguards need not be a single, homogeneous component. Indeed, some parts 841 of this document require a single safeguard be comprised of two or more 842 elements. For example, for thin insulation, two or more layers are required to 843 qualify as supplementary insulation. Another example is protective bonding 844 and protective earthing, both of which are comprised of wires, terminals, 845 screws, etc. 846
If a safeguard is comprised of two or more elements, then the function of the 847 safeguard should not be compromised by a failure of any one element. For 848 example, if a screw attaching a protective earthing wire should loosen, then 849 the current-carrying capacity of the protective earthing circuit may be 850 compromised, making its reliability uncertain. 851
4.4.3 Safeguard robustness 852
Rationale: Safeguards should be sufficiently robust to withstand the rigors of expected use 853 throughout the equipment lifetime. Robustness requirements are specified in the 854 various clauses. 855
4.4.3.4 Impact test 856
Rationale: Stationary equipment can, in some cases, be developed for a specific 857 installation in which it is not possible for certain surfaces to be subjected to an 858 impact when installed as intended. In those cases, the impact test is not 859 necessary when the installation makes clear that the side cannot be impacted. 860
4.4.3.6 Glass impact tests 861
Source: IEC 60065 862
Purpose: Verify that any glass that breaks does not cause skin-lacerating injury, or expose 863 class 3 hazards behind the glass. 864
Rationale: When it comes to glass, two hazards can be present in case the glass breaks: 865
− access to sharp edges from the broken glass itself 866
− exposure of class 3 energy hazards in case the glass is used as (part of) the 867 enclosure. 868
Should the glass break during the impact test, T.9 is applied to ensure the 869 expelled fragments will be at MS2 level or less. 870
Platen glass has a long history of being exempted, because it is quite obvious 871 for people that, if broken, the broken glass is hazardous and contact should be 872 avoided. There is no known history of serious injuries with this application. Platen 873 glass is the glass that is typically used in scanners, copiers, etc. Accidents are 874 rare, probably also because they are protected by an additional cover most of 875 the time, which limits the probability that an impact will occur on the glass. 876
CRTs are exempted because they have separate requirements. 877
The test value for floor standing equipment is higher because it is more likely to 878 be impacted by persons or carts and dollies at a higher force while in normal 879 use. 880
– 26 – 108/757/DC The exemption for glass below certain sizes is taken over from IEC 60065. There 881
is no good rationale to keep the exemption, other than that there are no serious 882 accidents known from the field. The HBSDT decided that they want to keep the 883 exemption in. 884
The flow chart in Figure 7 in this document shows the intent for the requirements. 885
886
Figure 7 – Flow chart showing the intent of the glass requirements 887
4.4.3.10 Compliance criteria 888
The value of 30 g for the weight limit is chosen based on the maximum dimension 889 of a side of 50 mm. A typical piece of glass with a size of 50 mm × 50 mm × 890 4 mm (roughly 2,80 g/cm3) would have a weight of around 30 g. 891
4.6 Fixing of conductors 892
Source: IEC 60950-1 893
Purpose: To reduce the likelihood that conductors could be displaced such that they 894 reduce the creepage distances and clearances. 895
Rationale: These requirements have been successfully used for products in the scope of 896 this document for many years. 897
For parts that are conductive but not intended to carry current, their displacement 898 should not defeat a safeguard, such as reducing a clearance or creepage 899 distance. 900
– 27 – 108/757/DC For example, a conductive screw fixing a radiator on a transistor in a class II 901
power supply should be such that it will not easily detach, because it could 902 eventually bridge a safety insulation. 903
4.7 Equipment for direct insertion into mains socket-outlets 904
Source: IEC 60065:2014, 15.5 ; IEC 60950-1:2013, 4.3.6; IEC 60335-1:2010, 22.3 and 905 IEC 60884-1:2013, 14.23.2 906
Purpose: Determine that equipment incorporating integral pins for insertion into mains 907 socket-outlets does not impose undue torque on the socket-outlet due to the 908 mass and configuration of the equipment. This type of equipment often is known 909 as direct plug-in equipment or direct plug-in transformers. 910
Rationale: Socket outlets are required to comply with the safety requirements in IEC 60884-911 1:2013, Plugs and socket-outlets for household and similar purposes – Part 1: 912 General requirements, including subclause 14.23.2. The requirements result in 913 socket designs with certain design limitations. Equipment incorporating integral 914 pins for insertion into mains socket-outlets is not allowed to exceed these design 915 limitations. 916
For direct plug-in equipment, including equipment for direct insertion into a 917 mains socket-outlet, normal use can be considered by representative testing. 918 The intent is not to require testing in all orientations. Subclause 4.1.6 is not 919 applicable unless the manufacturer specifically supplies instructions 920 representing multiple mounting positions or configurations. 921
4.8 Equipment containing coin / button cell batteries 922
Rationale: The determination whether the battery is unlikely to be removed by children due 923 to location within the equipment is an engineering judgment not requiring Annex 924 V. A coin / button cell battery located inside pluggable equipment without a 925 dedicated battery compartment is an example of a battery that would be 926 considered unlikely to be removed by children. 927
4.9 Likelihood of fire or shock due to entry of conductive objects 928
Purpose: The purpose of this subclause is to establish opening requirements that would 929 minimize the risk of foreign conductive objects falling into the equipment that 930 could bridge parts within class 2 or class 3 circuits, or between PS circuits that 931 could result in ignition or electric shock. 932
It is considered unlikely that a person would accidentally drop something that 933 could consequently fall into the equipment at a height greater than 1,8 m. 934
4.10.3 Power supply cords 935
Rationale: Power supply cords are neither internal nor external wiring. They are separately 936 covered in G.7. 937
_____________ 938
5 Electrically-caused injury 939
Purpose: Clause 5 classifies electrical energy sources and provides criteria for 940 determining the energy source class of each conductive part. The criteria for 941 energy source class include the source current-voltage characteristics, duration, 942 and capacitance. Each conductive part, whether current-carrying or not, or 943 whether earthed or not, shall be classed ES1, ES2, or ES3 with respect to earth 944 and with respect to any other simultaneously accessible conductive part. 945
240 VA limit 946
IEC 62368-1 does not have requirements for a 240 VA energy hazard that was 947 previously located in 2.1.1.5 of IEC 60950-1:2013. 948
– 28 – 108/757/DC
The origin/justification of the 240 VA energy hazard requirement in the legacy 949 documents was never precisely determined, and it appears the VA limits may 950 have come from a manufacturer’s specifications originally applied to exposed 951 bus bars in mainframe computers back in the 1960’s and concerns at the time 952 service personnel inadvertently bridging them with a metal part. 953
However, when IEC TC 108 started the IEC 62368-1 project the intent was to 954 take a fresh look at product safety using HBSE and only carry over a legacy 955 requirement if the safety science and HBSE justified it. After considerable study 956 by IEC TC 108, there was no support for carrying over the 240 VA requirement 957 since: 958
− the requirements were not based on any proven science or sound technical 959 basis; 960
− the 240 VA value was relatively arbitrary; and 961
− in practice the requirement was difficult to apply consistently (for example, on 962 a populated printed board or inside a switch mode power supply). 963
In the meantime, there are energy limits for capacitors in Clause 5, which 964 remains a more realistic concern and which were the second set of the energy 965 hazard requirements in IEC 60950-1, the first being steady state 240 VA. 966
In addition, there are other requirements in IEC 62368-1 that will limit exposure 967 to high levels of power (VA), including a VA limit for LPS outputs when those are 968 required by Annex Q (for outputs connected to building wiring as required by 969 6.5.2). 970
Electric burn (eBurn) 971
Analysis of the body current generated by increasing frequency sinusoidal 972 waveforms shows that the current continues to increase with frequency. The 973 same analysis shows that the touch current, which is discounted with 974 frequency, stabilizes. 975
The following paper describes the analysis fully: ‘Touch Current Comparison, 976 Looking at IEC 60990 Measurement Circuit Performance – Part 1: Electric Burn'; 977 Peter E Perkins; IEEE PSES Product Safety Engineering Newsletter, Vol 4, No 978 2, Nov 2008. 979
The crossover frequency is different for the startle-reaction circuit than for the 980 let go-immobilization circuit because of the separate Frequency Factor body 981 response curves related to current levels; analysis identifies the crossover 982 frequency where the eBurn current surpasses the touch current. Under these 983 conditions, a person touching the circuit will become immobilized and will not be 984 able to let go of the circuit. This crossover frequency is determined in the 985 analysis. The person contacting the circuit should always be able to let go. 986
The general conditions that apply to eBurn circuits are: 987
− the eBurn limit only applies to HF sinusoidal signals; 988
− the area of contact should be limited to a small, fingertip contact 989 (~ 1cm2); 990
− the contact time should be less than 1 s; at this short contact time, it is not 991 reasonable to define different levels for various persons; 992
− This requirement applies to accessible circuits that can be contacted at both 993 poles, including all grounded circuits isolated from the mains and any isolated 994 circuits where both contacts are easily available to touch. 995
A simplified application of these requirements in the documents limits the 996 accessibility of HF sinusoidal currents above a specified frequency. The 22 kHz 997 and 36 kHz frequency limits are where the eBurn current crosses the 5mA limit 998 for the ES1 and ES2 measurement circuits. This will ensure that the person 999 contacting the circuit will be able to remove themselves from the circuit under 1000 these conditions. 1001
– 29 – 108/757/DC
1 MHz limit 1002
The effects of electric current on the human body are described in the IEC 60479 1003 series and the requirements in IEC 62368-1 are drawn from there. The effects 1004 versus frequency are well laid out and properly accounted for in these 1005 requirements. The body effects move from conducted effects to surface 1006 radiofrequency burns at higher frequencies approaching 100 kHz. By long-term 1007 agreement, IEC safety documents are responsible for outlining the effects of 1008 current to 1 MHz, which are properly measured by the techniques given herein. 1009 Above the 1 MHz level, it becomes an EMC issue. Unless the current is provided 1010 as a principal action of the equipment operation, electric shock evaluation should 1011 not be needed above the 1 MHz level. Where it is fundamental to the equipment's 1012 operation, the high-frequency current levels shall be specially measured using 1013 proper high-frequency techniques, including classifying the circuits and, if 1014 necessary, appropriately protected to avoid any bodily injury. 1015
5.2.1 Electrical energy source classifications 1016
Source: IEC TS 60479-1:2005 and IEC 61201 1017
Purpose: To define the line between hazardous and non-hazardous electrical energy 1018 sources for normal operating conditions and abnormal operating conditions. 1019
Rationale: The effect on persons from an electric source depends on the current through 1020 the human body. The effects are described in IEC TS 60479-1. 1021
IEC TS 60479-1 (see Figures 20 and 22, Tables 11 and 13); zone AC-1 and 1022 zone DC-1; usually no reaction (Figure 8 and Figure 9, Table 2 and Table 3 in 1023 this document) is taken as values for ES1. 1024
IEC TS 60479-1 (see Figures 20 and 22; Tables 11 and 13); zone AC-2 and 1025 zone DC-2; usually no harmful physiological effects (see Figure 8 and Figure 9, 1026 Table 2 in this document) is taken as values for ES2. 1027
IEC TS 60479-1; zone AC-3 and zone DC-3; harmful physiological effects may 1028 occur (see Figure 8 and Figure 9, Table 2 and Table 3 in this document) is the 1029 ES3 zone. 1030
1031
1032
Figure 8 – Conventional time/current zones of effects 1033 of AC currents (15 Hz to 100 Hz) on persons for a current path corresponding 1034
to left hand to feet (see IEC TS 60479-1:2005, Figure 20) 1035
– 30 – 108/757/DC
Table 2 – Time/current zones for AC 15 Hz to 100 Hz 1036 for hand to feet pathway (see IEC TS 60479-1:2005, Table 11) 1037
Zones Boundaries Physiological effects
AC-1 up to 0,5 mA curve a Perception possible but usually no startle reaction
AC-2 0,5 mA up to curve b Perception and involuntary muscular contractions likely but usually no harmful electrical physiological effects
AC-3 Curve b and above Strong involuntary muscular contractions. Difficulty in breathing.
Reversible disturbances of heart function. Immobilisation may occur.
Effects increasing with current magnitude. Usually no organic damage to be expected.
AC-4a Above curve c1 Pathophysiological effects may occur such as cardiac arrest, breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c2 AC-4.1 Probability of ventricular fibrillation increasing up to about 5 %.
c2 – c3 AC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 AC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within the vulnerable period if the relevant thresholds are surpassed. As regards ventricular fibrillation, this figure relates to the effects of current that flows in the path left hand to feet. For other current paths, the heart current factor has to be considered.
1038
1039
Figure 9 – Conventional time/current zones of effects of DC currents on persons for 1040 a longitudinal upward current path (see IEC TS 60479-1:2005, Figure 22) 1041
– 31 – 108/757/DC
Table 3 – Time/current zones for DC for hand to feet pathway 1042 (see IEC TS 60479-1:2005, Table 13) 1043
Zones Boundaries Physiological effects
DC-1 Up to 2 mA curve a Slight pricking sensation possible when making, breaking or rapidly altering current flow.
DC-2 2 mA up to curve b Involuntary muscular contractions likely, especially when making, breaking or rapidly altering current flow, but usually no harmful electrical physiological effects
DC-3 curve b and above Strong involuntary muscular reactions and reversible disturbances of formation and conduction of impulses in the heart may occur, increasing with current magnitude and time. Usually, no organic damage to be expected.
DC-4a Above curve c1 Pathophysiological effects may occur such as cardiac arrest, breathing arrest, and burns or other cellular damage. Probability of ventricular fibrillation increasing with current magnitude and time.
c1 – c2 DC-4.1 Probability of ventricular fibrillation increasing up to about 5 %.
c2 – c3 DC-4.2 Probability of ventricular fibrillation up to about 50 %.
Beyond curve c3 DC-4.3 Probability of ventricular fibrillation above 50 %.
a For durations of current flow below 200 ms, ventricular fibrillation is only initiated within the vulnerable period if the relevant thresholds are surpassed. As regards ventricular fibrillation, this figure relates to the effects of current which flows in the path left hand to feet and for upward current. For other current paths, the heart current factor has to be considered.
1044
The seriousness of an injury increases continuously with the energy 1045 transferred to the body. To demonstrate this principle Figure 8 and Figure 9 1046 in this document (see IEC TS 60479-1, Figures 20 and 22) are transferred 1047 into a graph: effects vs energy (see Figure 10 in this document). 1048
1049
Figure 10 – Illustration that limits depend on both voltage and current 1050
Within the document, only the limits for Zone 1 (green) and Zone 2 (yellow) will 1051 be specified. 1052
Curve “a” (limit of Zone 1) will be the limit for parts accessible by an ordinary 1053 person during normal use. 1054
Curve “b” (limit of Zone 2) will be the limit for parts accessible by an ordinary 1055 person during (or after) a single fault. 1056
– 32 – 108/757/DC
IEC TC 108 regarded it not to be acceptable to go to the limits of either Zone 3 1057 or 4. 1058
In the document three (3) zones are described as electrical energy sources. 1059
This classification is as follows: 1060
− electrical energy source 1 (ES1): levels are of such a value that they do not 1061 exceed curve “a” (threshold of perception) of Figure 8 and Figure 9 in this 1062 document (see IEC TS 60479-1:2005, Figures 20 and 22). 1063
− electrical energy source 2 (ES2): levels are of such a value that they exceed 1064 curve “a”, but do not exceed curve “b” (threshold of let go) of Figure 8 and 1065 Figure 9 in this document (see IEC TS 60479-1:2005, Figures 20 and 22). 1066
− electrical energy source 3 (ES3): levels are of such a value that they exceed 1067 curve “b” of Figure 8 and Figure 9 in this document (see IEC 1068 TS 60479-1:2005, Figures 20 and 22). 1069
5.2.2.1 General 1070
When classifying a circuit or part that is not accessible, that circuit or part shall 1071 be regarded as being accessible when measuring prospective touch voltage 1072 and touch current. 1073
Signals for communication or data circuits are generally low voltage, high 1074 impedance sources. 1075
When combining these communication or data signals with a possible normal 1076 operating voltage (for example, DC feeding voltage), the communication or data 1077 signal voltage itself is disregarded and is not used for the classification of the 1078 circuits. If there is no normal operating voltage present, the signals are also 1079 disregarded for purposes of circuit classification. 1080
Examples for communication or data signals 1081
− typically found on indoor ICT networks, like USB, HDMI, PoE, Ethernet, 1082 analog voice, digital phone systems, G.fast, G.now, G.hn, ISDN-S Bus, A/V, 1083 etc. 1084
− typically found on outdoor and/or indoor ICT networks, like analog voice, 1085 T1/E1, SHDSL, xDSL, G.fast, G.now, G.hn, PoE, Ethernet, ISDN U interface, 1086 Primary rate ISDN, etc. 1087
NOTE 1 In this context, the normal operating voltage is the powering voltage for the ICT line. 1088
NOTE 2 See 5.2.2.6 for information regarding telephone ringing signals. 1089
5.2.2.2 Steady-state voltage and current limits 1090
Table 4 Electrical energy source limits for steady-state ES1 and ES2 1091
Source: IEC TS 60479-1:2005, Dalziel, Effect of Wave Form on Let-Go Currents; AIEE 1092 Electrical Engineering Transactions, Dec 1943, Vol 62. 1093
Rationale: The current limits of Table 4 line 1 and 2 are derived from curve a and b, Figure 8 1094 and Figure 9 in this document (see IEC TS 60479-1:2005, Figures 20 and 22). 1095
The basis for setting limits for combined AC and DC touch current is from the 1096 work of Dalziel which provides clear data for men, women and children. In the 1097 current diagram (Figure 22), the AC current is always the peak value (per 1098 Dalziel). In the voltage diagram (Figure 23), the 30 V AC and 50 V AC points on 1099 the baseline are recognized as AC RMS values as stated in Table 4. Since IEC 1100 TC 108 is working with consumer appliances, there is a need to provide 1101 protection for children, who are generally considered the most vulnerable 1102 category of people. The formulas of Table 4 address the Dalziel investigations. 1103
– 33 – 108/757/DC
Under single fault conditions of a relevant basic safeguard or supplementary 1104 safeguard, touch current is measured according to 5.1.2 of IEC 60990:2016. 1105 However, this IEC 60990 subclause references both the IEC 60990 1106 perception/reaction network (Figure 4) and the let-go network (Figure 5), 1107 selection of which depends on several factors. Figure 5 applies to touch current 1108 limits above 2 mA RMS. IEC TC 108 has decided that parts under single fault 1109 conditions of relevant basic safeguards or supplementary safeguards should 1110 be measured per Figure 5 (let-go immobilization network). Therefore, since 5.1.2 1111 makes reference to both Figure 4 and Figure 5, for clarification Table 4 is 1112 mentioned directly in 5.2.2.2. 1113
Because there is usually no reaction of the human body when touching ES1, 1114 access is permitted by any person (IEC TS 60479-1; zone AC-1 and zone DC-1). 1115
Because there may be a reaction of the human body when touching ES2, 1116 protection is required for an ordinary person. One safeguard is sufficient 1117 because there are usually no harmful physiological effects when touching ES2 1118 (IEC TS 60479-1:2005; zone AC-2 and zone DC-2). 1119
Because harmful physiological effects may occur when touching ES3, (IEC 1120 TS 60479-1:2005; zone AC-3 and zone DC-3), protection is required for an 1121 ordinary person and an instructed person, including after a fault of one 1122 safeguard. 1123
During the application of the electrical energy source limits for “combined AC 1124 and DC” in Table 4, if the AC component of a superimposed AC and DC energy 1125 source does not exceed 10 % of the DC energy, then the AC component can be 1126 disregarded for purposes of application of Table 4. This consideration is valid 1127 based on the definition of DC voltage in 3.3.14.1, which allows peak-to-peak 1128 ripple not exceeding 10 % of the average value to integrated into DC voltage 1129 considerations. As a result, in such cases where AC does not exceed 10 % of 1130 DC, only the DC energy source limits in Table 4 need be applied. 1131
When measuring combined AC and DC voltages and currents, both AC and DC 1132 measurements shall be made between the same points of reference. Do not 1133 combine common-mode measurements with differential-mode measurements. 1134 They shall be assessed separately. 1135
In using Table 4, ES1 touch current measurement specifies the startle-reaction 1136 circuit ‘a’ intended for limits less than 2 mA RMS / 2,8 mA peak and ES2 touch 1137 current specifies the let-go-immobilization circuit ‘b’ intended for limits > 2 mA 1138 RMS / 2,8 mA peak. These circuits are adopted from IEC 60990:2016, Clause 5. 1139
Normal operating conditions of equipment for touch current testing are 1140 outlined in 5.7.2 and Clause B.2 and includes operation of all operator controls. 1141 Abnormal operating conditions are specified in Clause B.3. Single fault 1142 conditions (within the equipment), specified in Clause B.4, includes faults of a 1143 relevant basic safeguard or a supplementary safeguard. 1144
5.2.2.3 Capacitance limits 1145
Table 5 Electrical energy source limits for a charged capacitor 1146
Source: IEC TS 61201:2007 (Annex A) 1147
Rationale: Where the energy source is a capacitor, the energy source class is determined 1148 from both the charge voltage and the capacitance. The capacitance limits are 1149 derived from IEC TS 61201:2007, see Table 4 in this document. 1150
The values for ES2 are derived from Table A.2 of IEC TS 61201:2007. 1151
The values for ES1 are calculated by dividing the values from Table A.2 of 1152 IEC TS 61201:2007 by two (2). 1153
– 34 – 108/757/DC
Table 4 – Limit values of accessible capacitance (threshold of pain) 1154
U
V
C
µF
U
kV
C
nF
70 42,4 1 8,0
78 10,0 2 4,0
80 3,8 5 1,6
90 1,2 10 0,8
100 0,58 20 0,4
150 0,17 40 0,2
200 0,091 60 0,133
250 0,061
300 0,041
400 0,028
500 0,018
700 0,012
1155
5.2.2.4 Single pulse limits 1156
Table 6 Voltage limits for single pulses 1157
Rationale: The values are based on the DC current values of Table 4, assuming 25 mA 1158 gives a voltage of 120 V DC (body resistance of 4,8 kΩ). The lowest value is 1159 taken as 120 V because, under single fault conditions, the voltage of ES1 can 1160 be as high as 120 V DC without a time limit. 1161
The table allows linear interpolation because the difference is considered to be 1162 very small. However, the following formula may be used for a more exact 1163 interpolation of the log-log based values in this table. The variable t or V is the 1164 desired unknown "in between value" and either may be determined when one is 1165 known: 1166
22 1
1
2
1
––
–1–
log loglog loglog logAntilog log log
log log
t tV Vt tV
t tt t
+ ×=
+ 1167
and 1168
22 1
1
2
1
––
–1–
log loglog loglog logAntilog log log
log log
V Vt tV V
tV VV V
+ ×=
+ 1169
where: 1170 t is the time duration that is required to be determined if Upeak voltage V 1171
is known (or t is known and V needs to be determined) 1172
t1 is the time duration adjacent to t corresponding to the Upeak voltage V1 1173
t2 is the time duration adjacent to t corresponding to the Upeak voltage V2 1174
V is the Upeak voltage value that is known if time duration t is to be 1175
determined (or V is required to be determined if time duration t is known) 1176
– 35 – 108/757/DC
V1 is the value of the voltage Upeak adjacent to V corresponding to time 1177
duration t1 1178
V2 is the value of the voltage Upeak adjacent to V corresponding to time 1179
duration t2 1180
Table 7 Current limits for single pulses 1181
Source: IEC TS 60479-1:2005 1182
Rationale: For ES1, the limit of single pulse should not exceed the ES1 steady-state voltage 1183 limits for DC voltages. 1184
For ES2, the voltage limits have been calculated by using the DC current values 1185 of curve b Figure 9 in this document and the resistance values of Table 10 of 1186 IEC TS 60479-1:2005, column for 5 % of the population (see Table 5 in this 1187 document). 1188
The current limits of single pulses in Table 7 for ES1 levels are from curve a and 1189 for ES2 are from curve b of Figure 9 in this document. 1190
The table allows linear interpolation because the difference is considered to be 1191 very small. However, the following formula may be used for a more exact 1192 interpolation of the log-log based values in this table. The variable t or I is the 1193 desired unknown "in between value" and either may be determined when one is 1194 known: 1195
1196
22 1
1
2
1
––
–1–
log loglog loglog logAntilog log log
log log
t tI It t
It tt t
+ ×=
+ 1197
and 1198
22 1
1
2
1
––
–1–
log loglog loglog logAntilog log log
log log
I It tI I
tI II I
+ ×=
+ 1199
where: 1200 t is the time duration that is required to be determined if the electric current 1201
I is known (or t is known and I needs to be determined) 1202
t1 is the time duration adjacent to t corresponding to the electric current I1 1203
t2 is the time duration adjacent to t corresponding to the electric current I2 1204
I is the value of the Ipeak current that is known if time duration t is to be 1205
determined (or I is required to be determined if time duration t is known) 1206
I1 is the value of the Ipeak adjacent to I corresponding to time duration t1 1207
I2 is the value of the Ipeak adjacent to I corresponding to time duration t2 1208
– 36 – 108/757/DC
Table 5 – Total body resistances RT for a current path hand to hand, DC, 1209
for large surface areas of contact in dry condition 1210
Touch voltage V
Values for the total body resistance RT (Ω)
that are not exceeded for
5 % of the population
50 % of the population
95 % of the population
25 50 75
100 125 150 175 200 225 400 500 700
1 000
2 100 1 600 1 275 1 100 975 875 825 800 775 700 625 575 575
3 875 2 900 2 275 1 900 1 675 1 475 1 350 1 275 1 225 950 850 775 775
7 275 5 325 4 100 3 350 2 875 2 475 2 225 2 050 1 900 1 275 1 150 1 050 1 050
Asymptotic value 575 775 1 050 NOTE 1 Some measurements indicate that the total body resistance RT for the current path hand to foot is somewhat lower than for a current path hand to hand (10 % to 30 %).
NOTE 2 For living persons the values of RT correspond to a duration of current flow of about 0,1 s. For longer durations RT values may decrease (about 10 % to 20 %) and after complete rupture of the skin RT approaches the initial body resistance Ro.
NOTE 3 Values of RT are rounded to 25 Ω.
1211
1212
5.2.2.6 Ringing signals 1213
Source: EN 41003 1214
Purpose: To establish limits for analogue telephone network ringing signals. 1215
Rationale: For details see rationale for Annex H. Where the energy source is an analogue 1216 telephone network ringing signal as defined in Annex H, the energy source class 1217 is taken as ES2 (as in IEC 60950-1:2005, Annex M). 1218
5.2.2.7 Audio signals 1219
Source: IEC 60065:2014 1220
Purpose: To establish limits for touch voltages for audio signals. 1221
Rationale: The proposed limits for touch voltages at terminals involving audio signals that 1222 may be contacted by persons have been extracted without deviation from 1223 IEC 60065. Reference: IEC 60065:2014, 9.1.1.2 a). Under single fault 1224 conditions, 10.2 of IEC 60065:2014 does not permit an increase in acceptable 1225 touch voltage limits. 1226
The proposed limits are quantitatively larger than the accepted limits of Table 5 1227 and Table 6, but are not considered dangerous for the following reasons: 1228
− the output is measured with the load disconnected (worst case load); 1229
– 37 – 108/757/DC
− defining the contact area of connectors and wiring is very difficult due to 1230 complex shapes. The area of contact is considered small due to the 1231 construction of the connectors; 1232
− normally, it is recommended to the user, in the instruction manual provided 1233 with the equipment, that all connections be made with the equipment in the 1234 “off” condition; 1235
− in addition to being on, the equipment would have to be playing some program 1236 at a high output with the load disconnected to achieve the proposed limits 1237 (although possible, highly unlikely). Historically, no known cases of injury are 1238 known for amplifiers with non-clipped output less than 71 V RMS; 1239
− the National Electrical Code (USA) permits accessible terminals with 1240 maximum output voltage of 120 V RMS. 1241
5.3.2 Accessibility to electrical energy sources and safeguards 1242
1243
What are the requirements between the non-accessible sources? 1244
Answer: None. As the enclosure is double insulated, the sources are not 1245 accessible. 1246
1247
Now there is an accessible connection. What are the requirements between the 1248 sources in this case? 1249
Answer: 1250
– Basic insulation between ES1 and ES2 1251
– Double insulation or reinforced insulation between ES1 and ES3 1252
– The insulation between ES2 and ES3 depends on the insulation between the 1253 ES1 and ES2 1254
– 38 – 108/757/DC
1255
Now there are two accessible connections from independent sources. What are 1256 the requirements between the sources in this case? 1257
Answer: 1258
– According to Clause B.4, the insulation or any components between the 1259 sources need to be shorted 1260
– If one of the two ES1 sources would reach ES2 levels basic safeguard 1261
– If both ES1 sources stay within ES1 limits no safeguard (functional 1262 insulation) 1263
For outdoor equipment, lower voltage limits apply because the body impedance 1264 is reduced to half the value when subjected to wet conditions as described in 1265 IEC TS 60479-1 and IEC TS 61201. 1266
Where Class III equipment is acceptable in an indoor application, this outdoor 1267 application does not introduce additional safeguard requirements. 1268
5.3.2.2 Contact requirements 1269
Source: IEC 61140:2001, 8.1.1 1270
Purpose: Determination of accessible parts for adults and children. Tests are specified in 1271 Annex V. 1272
Rationale: According to Paschen’s Law, air breakdown does not occur below 323 V peak or 1273 DC (at sea level). IEC 62368-1 uses 420 V peak (300 V RMS) to add an 1274 additional safety margin. 1275
5.3.2.3 Compliance criteria 1276
The reason for accepting different requirements for components is because you 1277 cannot expect your supplier to make different components for each end 1278 application. 1279
5.3.2.4 Terminals for connecting stripped wire 1280
Source: IEC 60065 1281
Purpose: To prevent contact of ES2 or ES3 parts. 1282
Rationale: Accepted constructions used in the audio/video industry for many years. 1283
5.4 Insulation materials and requirements 1284
Rationale: The requirements, test methods and compliance criteria are taken from the 1285 actual outputs from IEC TC 108 MT2 (formerly WG6) as well as from IEC TC 108 1286 MT1. 1287
– 39 – 108/757/DC
− The choice and application of components shall take into account the needs 1288 for electrical, thermal and mechanical strength, frequency of the working 1289 voltage and working environment (temperature, pressure, humidity and 1290 pollution). 1291
− Components shall have the electric strength, thermal strength, mechanical 1292 strength, dimensions, and other properties as specified in the document. 1293
− Depending on the grade of safeguard (basic safeguard, supplementary 1294 safeguard, reinforced safeguard) the requirements differ. 1295
− Components complying with their component documents (for example, 1296 IEC 60384-14 for capacitances) have to be verified for their application. 1297
− The components listed in this subclause of the new document have a 1298 separation function. 1299
5.4.1.1 Insulation 1300
Source: IEC 60664-1 1301
Purpose: Provide a reliable safeguard 1302
Rationale: Solid basic insulation, supplementary insulation, and reinforced insulation 1303 shall be capable of durably withstanding electrical, mechanical, thermal, and 1304 environmental stress that may occur during the anticipated lifetime of the 1305 equipment. 1306
Clearances and creepage distances may be divided by intervening 1307 unconnected (floating) conductive parts, such as unused contacts of a 1308 connector, provided that the sum of the individual distances meets the specified 1309 minimum requirements (see Figure O.4). 1310
5.4.1.4 Maximum operating temperatures for materials, components and systems 1311
Source: IEC 60085, IEC 60364-4-43, ISO 306, IEC 60695-10-2 1312
Rationale: Temperature limits given in Table 9: 1313
− limits for insulation materials including electrical insulation systems, including 1314 winding insulation (Classes A, E, B, F, H, N, R and 250) are taken from 1315 IEC 60085; 1316
− limits for insulation of internal and external wiring, including power supply 1317 cords with temperature marking are those indicated by the marking or the 1318 rating assigned by the (component) manufacturer; 1319
− limits for insulation of internal and external wiring, including power supply 1320 cords without temperature marking of 70 °C, are referenced in 1321 IEC 60364-4-43 for an ambient temperature of 25 °C; 1322
− limits for thermoplastic insulation are based on: 1323
• data from Vicat test B50 of ISO 306; 1324
• ball pressure test according to IEC 60695-10-2; 1325
• when it is clear from the examination of the physical characteristics of the 1326 material that it will meet the requirements of the ball pressure test; 1327
• experience with 125 °C value for parts in a circuit supplied from the mains. 1328
5.4.1.4.3 Compliance criteria 1329
Table 9 Temperature limits for materials, components and systems 1330
– 40 – 108/757/DC Rationale Regarding condition “a”, it has been assumed by the technical committee for 1331
many years that the thermal gradient between outer surface and inner windings 1332 will be limited to 10 °C differential as an average. As a result, the temperature 1333 limits for outer surface insulation measured via thermocouple is 10 °C lower than 1334 similar measurement with a thermocouple embedded in the winding(s), with both 1335 limits at least 5 °C less than the hot-spot temperature allowed per IEC 60085 as 1336 an additional safety factor. However, some modern transformer constructions 1337 with larger power densities may have larger thermal gradients, as may some 1338 outer surface transformer insulation thermal measurements in the 1339 equipment/system be influenced by forced cooling or similar effects. Therefore, 1340 if thermal imaging, computer modeling, or actual measurement shows a thermal 1341 gradient greater than 10 °C average between transformer surface temperature 1342 and transformer winding(s), the rise of resistance temperature measurement 1343 method and limits for an embedded thermocouple should be used (for example, 1344 100 °C maximum temperature for Class 105 (A)) for determining compliance of 1345 a transformer with Table 9 since the original assumptions do not hold true. 1346
As an example, a material rated for 124 °C using the rise of resistance method 1347 is considered suitable for classes whose temperature is lower (class with letter 1348 codes E and A) and not for classes whose temperature is higher (class with letter 1349 codes B, F, H, N, R and 250). 1350
5.4.1.5 Pollution degrees 1351
Source: IEC 60664-1 1352
Rationale: No values for PD 4 (pollution generates persistent conductivity) are included, as 1353 it is unlikely that such conditions are present when using products in the scope 1354 of the document. 1355
5.4.1.5.2 Test for pollution degree 1 environment and for an insulating compound 1356
The compliance check made by visual inspection applies both to single layer and 1357 multi-layer boards without the need for sectioning to check for voids, gaps, etc. 1358
5.4.1.6 Insulation in transformers with varying dimensions 1359
Source: IEC 60950-1 1360
Purpose: To consider actual working voltage along the winding of a transformer. 1361
Rationale: Description of a method to determine adequacy of solid insulation along the 1362 length of a transformer winding. 1363
5.4.1.7 Insulation in circuits generating starting pulses 1364
Source: IEC 60950-1, IEC 60664-1 1365
Purpose: To avoid insulation breakdown due to starting pulses. 1366
Rationale: This method has been successfully used for products in the scope of this 1367 document for many years. 1368
5.4.1.8 Determination of working voltage 1369
Source: IEC 60664-1:2020, 3.1.7; IEC 60950-1 1370
Rationale: The working voltage does not include short duration signals, such as transients. 1371 Recurring peak voltages are not included. Transient overvoltages are covered in 1372 the required withstand voltage. Ringing signals do not carry external 1373 transients. 1374
5.4.1.8.1 General 1375
Rationale: Functional insulation is not addressed in Clause 5, as it does not provide 1376 protection against electric shock. Requirements for functional insulation are 1377 covered in Clause 6, which addresses protection against electrically caused fire. 1378
Source: IEC 60664-1:2020, 3.1.14 1379
– 41 – 108/757/DC Rationale: In IEC 62368-1, “Circuit supplied from the mains” is used for a “primary circuit”. 1380
“Circuit isolated from the mains” is used for a “secondary circuit”. 1381
“External circuit” is defined as external to the equipment. ES1 can be external 1382 to the equipment. 1383
For an external circuit operating at ES2 level and not exiting the building, the 1384 transient is 0 V. Therefore, in this case, ringing peak voltage needs to be taken 1385 into account. 1386
5.4.1.8.2 RMS working voltage 1387
Source: IEC 60664-1:2020, 3.1.7 1388
Rationale: RMS working voltage is used when determining minimum creepage distance. 1389 Unless otherwise specified, working voltage is the RMS value. 1390
5.4.1.10 Thermoplastic parts on which conductive metallic parts are directly mounted 1391
Source: ISO 306 and IEC 60695-2 series 1392
Rationale: The temperature of the thermoplastic parts under normal operating conditions 1393 shall be 15 K less than the softening temperature of a non-metallic part. 1394 Supporting parts in a circuit supplied from the mains shall not be less than 1395 125 °C. 1396
5.4.2 Clearances 1397
5.4.2.1 General requirements 1398
Source: IEC 60664-1:2020 1399
Rationale: The dimension for a clearance is determined from the required impulse 1400 withstand voltage for that clearance. This concept is taken from 1401 IEC 60664-1:2020, 5.2. In addition, clearances are affected by the largest of the 1402 determined transients. The likelihood of simultaneous occurrence of transients 1403 is very low and is not taken into account. 1404
Overvoltages and transients that may enter the equipment, and peak voltages 1405 that may be generated within the equipment, do not break down the clearance 1406 (see IEC 60664-1:2020, 5.2.4 and 5.2.5). 1407
Minimum clearances of safety components shall comply with the requirements 1408 of their applicable component safety document. 1409
Clearances between the outer insulating surface of a connector and conductive 1410 parts at ES3 voltage level shall comply with the requirements of basic insulation 1411 only, if the connectors are fixed to the equipment, located internal to the outer 1412 electrical enclosure of the equipment, and are accessible only after removal 1413 of a sub-assembly that is required to be in place during normal operation. 1414
It is assumed that the occurrence of both factors, the sub-assembly being 1415 removed and the occurrence of a transient overvoltage, have a reduced 1416 likelihood and hazard potential. 1417
Source: IEC 60664-2 series, Application guide 1418
Rationale: The method is derived from the IEC 60664-2 series, Application guide. 1419
– 42 – 108/757/DC
Example: Assuming: – an SMPS power supply, – connection to the AC mains, – a peak of the working voltage (PWV) of 800 V, – frequencies above and below 30 kHz, – reinforced clearances required, – temporary overvoltages: 2 000 V Procedure 1: Table 10 requires 2,54 mm Table 11 requires 0,44 mm Result is 2,54 mm NOTE All PWV below 1 200 V have clearance requirements less than 3 mm for both Table 10 and Table 11
Procedure 2: Transients (OVC 2): 2 500 V RWV = 2 500 V Table 14 requires 3,0 mm The required ES test voltage according to Table 15 is 4,67 KV Result is 3,0 mm or ES test at 4,67 KV
Final result: – 3,0 mm or – ES test at 4,67 KV and 2,54 mm ATTENTION: For a product with connection to coax cable, different values are to be used since a different transient and required withstand voltage is required.
1420
– 43 – 108/757/DC 5.4.2.2 Procedure 1 for determining clearance 1421
Rationale: Related to the first dash of 5.4.2.2, it is noted that an example of a cause of 1422 determination of the peak value of steady state voltages that are below the peak 1423 voltage of the mains includes, for example, a determination in accordance with 1424 the 2nd and 3rd dash of 5.4.2.3.3 where filtering is in place to lower expected 1425 peak voltages. 1426
Similarly, related to the second dash of 5.4.2.2, an example of this case where 1427 the recurring peak voltage is limited to 1,1 times the mains voltage may be use 1428 of certain forms of surge protection devices that reduce overvoltage category. 1429
Peak of the working voltage versus recurring peak voltage. 1430
There has been some discussion between the two terms. The peak of the 1431 working voltage is the peak value of the waveform that occurs each cycle, and 1432 therefore is considered to be a part of the working voltage. 1433
A recurring peak voltage is a peak that does not occur at each cycle of the 1434 waveform, but that reoccurs at a certain interval, usually at a lower frequency 1435 than the waveform frequency. 1436
Figure 11 in this document gives an example of a waveform where the recurring 1437 peak voltage occurs every two cycles of the main waveform. 1438
1439
Figure 11 – Illustration of working voltage 1440
Table 10 Minimum clearances for voltages with frequencies up to 30 kHz 1441
Rationale: IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for reinforced 1442 clearance, some values were more than double the requirements for basic 1443 insulation. IEC TC 108 felt that this should not be the case and decided to limit 1444 the requirement for reinforced insulation to twice the value of basic insulation, 1445 thereby deviating from IEC 60664-1. 1446
In addition, normal rounding rules were applied to the values in the table. 1447
5.4.2.3.2.2 Determining AC mains transient voltages 1448
Source: IEC 60664-1:2020, 4.3.2 1449
Rationale: Table 12 is derived from Table F.1 of IEC 60664-1:2020. 1450
The term used in IEC 60664-1 is ‘rated impulse voltage’. Products covered by 1451 IEC 62368-1 are also exposed to transients from external circuits, and 1452 therefore another term is needed, to show the different source. 1453
Outdoor equipment that is part of the building installation, or that may be 1454 subject to transient overvoltages exceeding those for Overvoltage Category II, 1455 shall be designed for Overvoltage Category III or IV, unless additional protection 1456 is to be provided internally or externally to the equipment. In this case, the 1457 installation instructions shall state the need for such additional protection. 1458
– 44 – 108/757/DC 5.4.2.3.2.3 Determining DC mains transient voltages 1459
Rationale: Transient overvoltages are attenuated by the capacitive filtering. 1460
5.4.2.3.2.4 Determining external circuit transient voltages 1461
Source: ITU-T K.21 1462
Rationale: Transients have an influence on circuits and insulation, therefore transients on 1463 external circuits need to be taken into account. Transients are needed only for 1464 the dimensioning safeguards. Transients should not be used for the 1465 classification of energy sources (ES1, ES2, etc.). 1466
It is expected that external circuits receive a transient voltage of 1,5 kV peak 1467 with a waveform of 10/700µs from sources outside the building. 1468
The expected transient is independent from the application (telecom; LAN or 1469 other). Therefore, it is assumed that for all kinds of applications the same 1470 transient appears. The value 1,5 kV 10/700µs is taken from ITU-T K.21. 1471
It is expected that external circuits using earthed coaxial cable receive no 1472 transients that have to be taken into account from sources outside the building. 1473
Because of the earthed shield of the coaxial cable, a possible transient on the 1474 outside cable will be reduced at the earthed shield at the building entrance of 1475 the cable. 1476
It is expected that for external circuits within the same building no transients 1477 have to be taken into account. 1478
The transients for an interface are defined with respect to the terminals where 1479 the voltage is defined. For the majority of cases, the relevant voltages are 1480 common (Uc) and differential mode (Ud) voltages at the interface. For hand-held 1481
parts or other parts in extended contact with the human body, such as a 1482 telephone hand set, the voltage with respect to local earth (Uce) may be relevant. 1483
Figure 12 in this document shows the definition of the various voltages for 1484 paired-conductor interface. 1485
The transients for coaxial cable interfaces are between the centre conductor and 1486 shield (Ud) of the cable if the shield is earthed at the equipment. If the shield is 1487
isolated from earth at the equipment, then the shield-to-earth voltage (Us) is 1488
important. Earthing of the shield can consist of connection of the shield to the 1489 protective earthing, functional earth inside or immediately outside the 1490 equipment. It is assumed that all earths are bonded together. Figure 13 in this 1491 document shows the definition of the various voltages for coaxial-cable 1492 interfaces. 1493
An overview of insulation requirements is given in Table 6 in this document. 1494
1495
– 45 – 108/757/DC
1496
1497
Figure 12 – Illustration of transient voltages on paired conductor external circuits 1498
– 46 – 108/757/DC
1499
1500
Figure 13 – Illustration of transient voltages on coaxial-cable external circuits 1501
Table 6 – Insulation requirements for external circuits 1502
External Circuit under consideration
Insulation Requirement
ES1 earthed None None
ES1 unearthed Separation (to floating metal parts and other floating ES1 circuits)
Electric strength test (using Table 15) between unearthed ES1 and other unearthed ES1 and floating parts
ES2 Basic insulation (to ES1 and metal parts)
Clearances; creepage distance; and solid insulation and by electric strength test (using Table 15) between ES2 and ES1 and metal parts
ES3 Double insulation or reinforced insulation (to ES1, ES2 and metal parts)
Clearances; creepage distance; and solid insulation requirements including electric strength test (using Table 15)
1503
– 47 – 108/757/DC Table 13 External circuit transient voltages 1504
Rationale: When the DC power distribution system is located outside the building, transient 1505 over-voltages can be expected. Transients are not present if the DC power 1506 system is connected to protective earthing and is located entirely within a 1507 single building. 1508
Sources: ID1a, ID1b and ID1c: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102 1509
ID2: IEC 62368-1:2022 (4th edition) 1510
ID3a: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102. See also IEC 1511 60728-11 for isolation devices and IEC TR 62101 for Network Environment 1512 definitions. 1513
ID3b: IEC 61000-4-5, ITU K.21, K.44 and K.45 and IEC TR 62102. It should be 1514 noted that these documents recommend 1000 V 1.2/50 (earthed applications), 1515 1000 V 10/700 (unearthed applications). 1516
Voltage is center conductor to shield/earth/conductive exposed parts and shield 1517 to earth/other conductive parts 1518
Based on historical precedence for safety, these transient exposure levels may 1519 be considered low enough that no special design criteria need to be evaluated 1520 or transients taken into account. 1521
ID3c: IEC 62368-1:202x. This aligns also with IEC 61000-4-5, where < 10 m 1522 ports and interconnect ports and network environment 0 definition. 1523
5.4.2.3.2.5 Determining transient voltage levels by measurement 1524
Source: Test method is taken from IEC 60950-1:2013, Annex G. 1525
5.4.2.3.4 Determining clearances using required withstand voltage 1526
Source: IEC 60664-1:2020, Table F.2 Case A (inhomogeneous field) and Case B 1527 (homogeneous field) 1528
Rationale: Values in Table 14 are taken from IEC 60664-1:2020 Table F.2 Case A 1529 (inhomogeneous field) and Case B (homogeneous field) and include explicit 1530 values for reinforced insulation. Clearances for reinforced insulation have 1531 been calculated in accordance with 5.2.5 of IEC 60664-1:2020. For reinforced 1532 insulation 5.2.5 states clearance shall be to the corresponding rated impulse 1533 voltage that is one step higher for voltages in the preferred series. For voltages 1534 that are not in the preferred series, the clearance should be based on 160 % of 1535 the required withstand voltage for basic insulation. 1536
When determining the required withstand voltage, interpolation should be 1537 allowed when the internal repetitive peak voltages are higher than the mains 1538 peak voltages, or if the required withstand voltage is above the mains transient 1539 voltage values. 1540
No values for PD 4 (pollution generates persistent conductivity) are included, as 1541 it is unlikely that such conditions are present when using products in the scope 1542 of the document. 1543
Table 14 Minimum clearances using required withstand voltage 1544
Rationale: IEC 62368-1 follows the rules and requirements of IEC basic safety publications, 1545 one of which is the IEC 60664 series. IEC 60664-1 specifies clearances for 1546 basic insulation and supplementary insulation. Clearances for reinforced 1547 insulation are not specified. Instead, 5.1.6 specifies the rules for determining 1548 the reinforced clearances. 1549
The reinforced clearances in Table 14 have a varying slope, and include a 1550 “discontinuity”. The values of Table 14 are shown in Figure 14 in this document. 1551
– 48 – 108/757/DC
1552
Figure 14 – Basic and reinforced insulation in Table 14; 1553 ratio reinforced to basic 1554
The brown line, reinforced clearance, is not a constant slope as is the yellow 1555 line, basic clearance. The ratio of reinforced to basic (blue line) varies from a 1556 maximum of 2:1 to a minimum of 1,49:1. Physically, this is not reasonable; the 1557 ratio should be nearly constant. 1558
In IEC 60664-1:2020, the values for basic insulation are given in Table F.2. No 1559 values are given for reinforced insulation. Table F.2 refers to 5.2.5 for 1560 reinforced insulation. 1561
Rule 1, preferred series impulse withstand voltages 1562
Subclause 5.2.5 of IEC 60664-1:2020 states: 1563
“With respect to impulse withstand voltages, clearances of reinforced 1564 insulation shall be dimensioned as specified in Table F.2 corresponding to the 1565 rated impulse withstand voltage but one step higher in the preferred series of 1566 values in 4.2.2.1 than that specified for basic insulation.” 1567
NOTE 1 IEC 62368-1 uses the term “required withstand voltage” instead of the IEC 60664-1 1568 term “required impulse withstand voltage.” 1569
NOTE 2 IEC 62368-1 uses the term “mains transient voltage” instead of the IEC 60664-1 term 1570 “rated impulse voltage.” 1571
The preferred series of values of rated impulse voltage according to 4.2.3 of 1572 IEC 60664-1:2007 is: 330 V, 500 V, 800 V, 1 500 V, 2 500 V, 4 000 V, 6 000 V, 1573 8 000 V, 12 000 V 1574
Applying Rule 1, the reinforced clearance (inhomogeneous field, pollution 1575 degree 2, Table F.2) for: 1576
– 330 V would be the basic insulation clearance for 500 V: 0,2 mm 1577
– 500 V would be the basic insulation clearance for 800 V: 0,2 mm 1578
– 800 V would be the basic insulation clearance for 1 500 V: 0,5 mm 1579
– 49 – 108/757/DC
– 1 500 V would be the basic insulation clearance for 2 500 V: 1,5 mm 1580
– 2 500 V would be the basic insulation clearance for 4 000 V: 3,0 mm 1581
– 4 000 V would be the basic insulation clearance for 6 000 V: 5,5 mm 1582
– 6 000 V would be the basic insulation clearance for 8 000 V: 8,0 mm 1583
– 8 000 V would be the basic insulation clearance for 12 000 V: 14 mm 1584
– 12 000 V is indeterminate because there is no preferred voltage above 1585 12 000 volts. 1586
Rule 2, 160 % of impulse withstand voltages other than the preferred series 1587
With regard to non-mains circuits, subclause 5.2.5 of IEC 60664-1:2020 states: 1588
“If the impulse withstand voltage required for basic insulation according to 1589 4.2.2.1 is other than a value taken from the preferred series, reinforced 1590 insulation shall be dimensioned to withstand 160 % of the impulse withstand 1591 voltage required for basic insulation.” 1592
The impulse withstand voltages other than the preferred series (in IEC 60664-1593 1:2020, Table F.2) are: 400 V, 600 V, 1 200 V, 2 000 V, 3 000 V, 10 000 V, and 1594 all voltages above 12 000 V. 1595
Applying Rule 2, the reinforced clearance (inhomogeneous field, pollution 1596 degree 2, Table F.2) for: 1597
400 V x 1,6 = 640 V interpolated to 0,20 mm. 1598
Since 640 V is not in the list, the reinforced insulation is determined by 1599 interpolation. Interpolation yields the reinforced clearance as 0,2 mm. 1600
Applying Rule 2 to the impulse withstand voltages in Table F.2 that are not in 1601 the preferred series: 1602
– 400 V × 1,6 = 640 V interpolated to 0,20 mm 1603
– 600 V × 1,6 = 960 V interpolated to 0,24 mm 1604
– 1 200 V × 1,6 = 1 920 V interpolated to 0,92 mm 1605
– 2 000 V × 1,6 = 1 320 V interpolated to 2,2 mm 1606
– 3 000 V × 1,6 = 4 800 V interpolated to 3,8 mm 1607
– 10 000 V × 1,6 = 13 000 V interpolated to 19,4 mm 1608
– 15 000 V to 100 000 V × 1,6 and interpolated according to the rule. 1609
Clearance differences for Rules 1 and 2 1610
The two rules, Rule 1 for impulse withstand voltages of the preferred series, and 1611 Rule 2 for impulse withstand voltages other than the preferred series, yield 1612 different clearances for the same voltages. These differences occur because 1613 the slope, mm/kV, of the two methods is slightly different. The slope for Rule 1 1614 is not constant. The slope for Rule 2 is nearly constant. Figure 15 in this 1615 document illustrates the differences between Rule 1, Rule 2 and Table 14 of 1616 IEC 62368-1. 1617
– 50 – 108/757/DC
1618
Figure 15 – Reinforced clearances according to Rule 1, Rule 2, and Table 14 1619
If the two values for Rules 1 and 2 are combined into one set of values, the 1620 values are the same as in existing Table 14 (the brown line in Figure 14 and 1621 Figure 15 in this document). According to IEC 60664-1:2020, 5.2.5, only the 1622 impulse withstand voltages “other than a value taken from the preferred series…” 1623 are subject to the 160 % rule. Therefore, the clearances jump from Rule 1 1624 criteria to Rule 2 criteria and back again. This yields the radical slope changes 1625 of the Table 14 reinforced clearances (brown) line. 1626
Physically, the expected reinforced insulation clearances should be a constant 1627 proportion of the basic insulation clearances. However, the proportion between 1628 steps of Rule 1 (preferred series of impulse withstand voltages) are: 1629
– 330 V to 500 V: 1,52 1630
– 500 V to 800 V: 1,60 1631
– 800 V to 1 500 V: 1,88 1632
– 1 500 V to 2 500 V: 1,67 1633
– 2 500 V to 4 000 V: 1,60 1634
– 4 000 V to 6 000 V: 1,50 1635
– 6 000 V to 8 000 V: 1,33 1636
– 8 000 V to 12 000 V: 1,50 1637
Average proportion, 330 to 12 000: 1,57 1638
For Rule 2, all of the clearances for reinforced insulation are based on exactly 1639 1,6 times the non-preferred series impulse withstand voltage for basic 1640 insulation. 1641
The two rules applied in accordance with 5.2.5 of IEC 60664-1:2020 result in the 1642 variable slope of the clearance requirements for reinforced insulation of 1643 IEC 62368-1. 1644
Rule 1 Rule 2 Basic insulation Table 15
– 51 – 108/757/DC
IEC TC 108 noted that, if the rules of IEC 60664-1 are followed, for clearances 1645 for reinforced insulation, some values were more than double the requirements 1646 for basic insulation. IEC TC 108 felt that this should not be the case and 1647 decided to limit the requirement for reinforced insulation to twice the value of 1648 basic insulation, thereby deviating from IEC 60664-1. 1649
In addition, normal rounding rules were applied to the values in the table. 1650
5.4.2.4 Determining the adequacy of a clearance using an electric strength test 1651
Source: IEC 60664-1:2020, Table F.6 1652
Purpose: Tests are carried out by either impulse voltage or AC voltage with the values of 1653 Table 15. 1654
Rationale: The impulse test voltages in Table 15 are taken from IEC 60664-1:2020, 1655 Table F.6. The calculation for the AC RMS. values as well as the DC values are 1656 based on the values given in Table A.1 of IEC 60664-1:2020 (see Table 7 in this 1657 document for further explanation). 1658
This test is not suited for homogenous fields. This is for an actual design that is 1659 within the limits of the homogenous and inhomogeneous field. 1660
Calculations for the voltage drop across an air gap during the electric strength 1661 test may be rounded up to the next higher 0,1 mm increment. In case the 1662 calculated value is higher than the value in the next row, the next row may be 1663 used. 1664
Enamel Material: Most commonly used material is polyester resin or polyester 1665
Dielectric constant for Polyester: 5 (can vary) 1666
Dielectric constant for air: 1 1667
Formula used for calculation (voltage divides inversely proportional to the 1668 dielectric constant) 1669
Transient = 2 500 V = 2 500 (thickness of enamel / 5 + air gap / 1) = 2 500 (0,04 1670 / 5 + 2 / 1 for 2 mm air gap) = 2 500 (0,008 + 2) = (10 V across enamel + 2 490 V 1671 across air gap) 1672
Related to condition a of Table 15, although U is any required withstand 1673 voltage higher than 12,0 kV, there is an exception when using Table F.6 of 1674 IEC 60664-1:2020. 1675
– 52 – 108/757/DC
Table 7 – Voltage drop across clearance and solid insulation in series 1676
Enamel thickness
mm
Air gap
mm
Transient on 240 V system
Transient voltage
across air gap
Transient voltage across enamel
Peak impulse
test voltage for
2 500 V peak
transient from
Table 16
Test voltage
across air gap
Test voltage across enamel
Material: Polyester, dielectric constant = 5
0,04 2 2 500 2 490 10 2 950 12 2 938
0,04 1 2 500 2 480 20 2 950 24 2 926
0,04 0,6 2 500 2 467 33 2 950 39 2 911
For 2 500 V peak impulse (transient for 230 V system), the homogenous field distance is 0,6 mm (from Table A.1 of IEC 60664-1:2020). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,79 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test. This gives us a margin of (0,19/0,6) × 100 = 3,2 %. In actual practice, the distance will be higher as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the conservative side.
Material: Polyamide, dielectric constant = 2,5
0,04 2 2 500 2 480 20 2 950 23 2 927
0,04 1 2 500 2 460 40 2 950 46 2 904
0,04 0,6 2 500 2 435 65 2 950 76 2 874
For 2 500 V peak impulse (transient for 230 V system), the homogenous field distance is 0,6 mm (from Table A.1 of IEC 60664-1:2020). Our test voltage for 2 500 V peak is 2 950 V peak from Table 15. This means that a minimum distance of 0,78 mm through homogenous field needs to be maintained to pass the 2 950 V impulse test. This gives us a margin of (0,18/0,6) × 100 = 3,0 %. In actual practice, the distance will be higher, as it is not a true homogenous field. Therefore, we do not need to verify compliance with Table 14. We are always on the conservative side.
1677
5.4.2.5 Multiplication factors for altitudes higher than 2 000 m above sea level 1678
Source: IEC 60664-1:2020, curve number 2 for case A using impulse test. 1679
Purpose: Test is carried out by either impulse voltage or AC voltage with the values of 1680 Table 16 and the multiplication factors for altitudes higher than 2 000 m. 1681
Rationale: Table 16 is developed using Figure A.1 of IEC 60664-1:2020, curve number 2 1682 for case A using impulse test. 1683
5.4.2.6 Compliance criteria 1684
Source: IEC 60664-1:2020, 5.2 1685
Rationale: IEC 62368-1, Annex O figures are similar/identical to figures in 1686 IEC 60664-1:2020. 1687
Tests of Annex T simulate the occurrence of mechanical forces: 1688
− 10 N applied to components and parts that may be touched during operation 1689 or servicing. Simulates the accidental contact with a finger or part of the hand; 1690
− 30 N applied to internal enclosures and barriers that are accessible to 1691 ordinary persons. Simulates accidental contact of part of the hand; 1692
− 100 N applied to external enclosures of transportable equipment and 1693 handheld equipment. Simulates expected force applied during use or 1694 movement; 1695
− 250 N applied to external enclosures (except those covered in T.4). 1696 Simulates expected force applied by a body part to the surface of the 1697 equipment. It is not expected that such forces will be applied to the bottom 1698 surface of heavy equipment (> 18 kg). 1699
– 53 – 108/757/DC During the force tests metal surfaces shall not come into contact with parts at 1700
ES2 or ES3 voltage. 1701
5.4.3 Creepage distances 1702
Source: IEC 60664-1:2020, 3.1.5 1703
Purpose: To prevent flashover along a surface or breakdown of the insulation. 1704
Rationale: Preserve safeguard integrity. 1705
In IEC 60664-1:2020, Table F.5 columns 2 and 3 for printed wiring boards are 1706 deleted, as there is no rationale for the very small creepage distances for 1707 printed wiring in columns 2 and 3 (the only rationale is that it is in the basic safety 1708 publication IEC 60664-1). 1709
However, there is no rationale why the creepage distances are different for 1710 printed wiring boards and other isolation material under the same condition 1711 (same PD and same CTI). 1712
Moreover the creepage distances for printed boards in columns 2 and 3 are in 1713 conflict with the requirements in G.13.3 (Coated printed boards). Consequently 1714 the values for voltages up to 455 V in Table G.16 were replaced. 1715
Creepage distances between the outer insulating surface of a connector and 1716 conductive parts at ES3 voltage level shall comply with the requirements of basic 1717 insulation only, if the connectors are fixed to the equipment, located internal to 1718 the outer electrical enclosure of the equipment, and are accessible only after 1719 removal of a sub-assembly which is required to be in place during normal 1720 operation. 1721
It is assumed that the occurrence of both factors, the sub-assembly being 1722 removed, and the occurrence of a transient overvoltage have a reduced 1723 likelihood and hazard potential. 1724
5.4.3.2 Test method 1725
Source: IEC 60664-1:2020, 3.1.4 1726
Purpose: Measurement of creepage distance. 1727
Rationale: To preserve safeguard integrity after mechanical tests. 1728
Annex O figures are similar/identical to figures in IEC 60950-1 and IEC 60664-1. 1729
Tests of Annex T simulate the occurrence of mechanical forces: 1730
− 10 N applied to components and parts that are likely to be touched by a 1731 skilled person during servicing, where displacement of the part reduces the 1732 creepage distance. Simulates the accidental contact with a finger or part of 1733 the hand. 1734
− 30 N applied to internal enclosures and barriers that are accessible to 1735 ordinary persons. Simulates accidental contact of part of the hand. 1736
− 100 N applied to external enclosures of transportable equipment and 1737 hand-held equipment. Simulates expected force applied during use or 1738 movement. 1739
− 250 N applied to external enclosures (except those covered in T.4). 1740 Simulates expected force when leaning against the equipment surface. It is 1741 not expected that such forces will be applied to the bottom surface of heavy 1742 equipment (> 18 kg). 1743
Creepage distances are measured after performing the force tests of Annex T. 1744
5.4.3.3 Material group and CTI 1745
Source: IEC 60112 1746
Rationale: Classification as given in IEC 60112. 1747
– 54 – 108/757/DC 5.4.3.4 Compliance criteria 1748
Source: IEC 60664-1:2020, Table F.5; IEC 60664-4 for frequencies above 30 kHz 1749
Rationale: Values in Table 17 are the same as in Table F.5 of IEC 60664-1:2020. 1750
Values in Table 18 are the same as in Table 2 of IEC 60664-4:2005 and are used 1751 for frequencies up to 400 kHz. 1752
5.4.4 Solid insulation 1753
Source: IEC 60950-1, IEC 60664-1 1754
Purpose: To prevent breakdown of the solid insulation. 1755
Rationale: To preserve safeguards integrity. 1756
Exclusion of solvent based enamel coatings for safety insulations are based on 1757 field experience. However, with the advent of newer insulation materials those 1758 materials may be acceptable in the future when passing the adequate tests. 1759
Except for printed boards (see G.13), the solid insulation shall meet the 1760 requirements of 5.4.4.4 to 5.4.4.7 as applicable. 1761
5.4.4.2 Minimum distance through insulation 1762
Source: IEC 60950-1:2005 1763
Purpose: Minimum distance through insulation of 0,4 mm for supplementary insulation 1764 and reinforced insulation. 1765
Rationale: Some (very) old documents required for single insulations 2 mm dti (distance 1766 through insulation) for reinforced insulation and 1 mm for supplementary 1767 insulation. If this insulation served also as outer enclosure for Class II 1768 equipment, it had to be mechanically robust, which was tested with a hammer 1769 blow of 0,5 Nm. 1770
The wire documents did not distinguish between grades of insulation, and 1771 required 0,4 mm for PVC insulation material. This value was considered 1772 adequate to protect against electric shock when touching the insulation if it was 1773 broken. This concept was also introduced in VDE 0860 (which evolved into 1774 IEC 60065), where the 0,4 mm value was discussed first. For IT products this 1775 value was first only accepted for in accessible insulations. 1776
The VDE document for telecom equipment (VDE 0804) did not include any 1777 thickness requirements, but the insulation had to be adequate for the application. 1778
The document VDE 0730 for household equipment with electric motors 1779 introduced in 1976 the requirement of an insulation thickness of 0,5 mm between 1780 input and output windings of a transformer. This was introduced by former 1781 colleagues from IBM and Siemens (against the position of the people from the 1782 transformer committee). 1783
Also VDE 0110 (Insulation Coordination, which evolved into the IEC 60664 1784 series) contained a minimum insulation thickness of 0,5 mm for 250 V supply 1785 voltage, to cover the effect of insulation breakage. 1786
These 0,5 mm then evolved into 0,4 mm (in IEC 60950-1), with the reference to 1787 VDE 0860 (IEC 60065), where this value was already in use. 1788
It is interesting to note that the 0,31 mm which is derived from Table 2A of 1789 IEC 60950-1, has also a relation to the 0,4 mm. 0,31 mm is the minimum value 1790 of the average insulation thickness of 0,4 mm, according to experts from the wire 1791 manufacturers. 1792
– 55 – 108/757/DC 5.4.4.3 Insulating compound forming solid insulation 1793
Source: IEC 60950-1 1794
Purpose: Minimum distance through insulation of 0,4 mm for supplementary insulation 1795 and reinforced insulation. 1796
Rationale: The same distance through insulation requirements as for solid insulation apply 1797 (see 5.4.4.2). Insulation is subjected to thermal cycling (see 5.4.1.5.3), humidity 1798 test (see 5.4.8) and electric strength test (see 5.4.9). Insulation is inspected for 1799 cracks and voids. 1800
5.4.4.4 Solid insulation in semiconductor devices 1801
Source: IEC 60950-1, UL 1577 1802
Purpose: No minimum thickness requirements for the solid insulation. 1803
Rationale: – type testing of 5.4.9.1 (electric strength testing at 160 % of the normal 1804 value after thermal cycling and humidity conditioning), and routine 1805 electric strength test of 5.4.9.2 has been used for many years, especially 1806 in North America. 1807
– refers to G.12, which references IEC 60747-5-5. 1808
5.4.4.5 Insulating compound forming cemented joints 1809
Source: IEC 60950-1 1810
Rationale: a) The distances along the path comply with PD 2 requirements irrespective of 1811 the joint; 1812
b) applies if protected to generate PD 1 environment; 1813 c) applies if treated like solid insulation environment, no clearances and 1814
creepage distances apply; 1815 d) is not applied to printed boards, when the board temperature is below 90 °C, 1816
as the risk for board delaminating at lower temperatures is considered low. 1817
Optocouplers are excluded from the requirements of this subclause, because the 1818 document requires optocouplers to comply with IEC 60747-5-5, which sufficiently 1819 covers cemented joints. 1820
5.4.4.6.1 General requirements 1821
Source: IEC 60950-1, IEC 61558-1:2005 1822
Rationale: No dimensional or constructional requirements for insulation in thin sheet 1823 material used as basic insulation, is aligned to the requirements of 1824 IEC 61558-1. 1825
Two or more layers with no minimum thickness are required for supplementary 1826 insulation or reinforced insulation, provided they are protected against 1827 external mechanical influences. 1828
Each layer is qualified for the full voltage for supplementary insulation or 1829 reinforced insulation. 1830
The requirements are based on extensive tests performed on thin sheet material 1831 by manufacturers and test houses involved in IEC TC 74 (now IEC TC 108) work. 1832
5.4.4.6.2 Separable thin sheet material 1833
Source: IEC 60950-1 1834
Rationale: For two layers, test each layer with the electric strength test of 5.4.9 for the 1835 applicable insulation grade. For three layers, test all combinations of two layers 1836 together with the electric strength test of 5.4.9 for the applicable insulation grade. 1837
Each layer is qualified for the full voltage for supplementary insulation or 1838 reinforced insulation. 1839
– 56 – 108/757/DC The requirements are based on extensive tests performed on thin sheet material 1840
by manufacturers and test houses involved in IEC TC 74 (now IEC TC 108) work. 1841
5.4.4.6.3 Non-separable thin sheet material 1842
Source: IEC 60950-1 1843
Rationale: For testing non-separable layers, all the layers are to have the same material 1844 and thickness. If not, samples of different materials are tested as given in 1845 5.4.4.6.2 for separable layers. When testing non-separable layers, the principle 1846 used is the same as for separable layers. 1847
When testing two separable layers, each layer is tested for the required test 1848 voltage. Two layers get tested for two times the required test voltage as each 1849 layer is tested for the required test voltage. When testing two non-separable 1850 layers, the total test voltage remains the same, for example, two times the 1851 required test voltage. Therefore, two non-separable layers are tested at 200 % 1852 of the required test voltage. 1853
When testing three separable layers, every combination of two layers is tested 1854 for the required test voltage. Therefore, a single layer gets tested for half the 1855 required test voltage and three layers are tested for 150 % of the required test 1856 voltage. 1857
5.4.4.6.4 Standard test procedure for non-separable thin sheet material 1858
Source: IEC 60950-1 1859
Rationale: Test voltage 200 % of Utest if two layers are used. 1860
Test voltage 150 % of Utest if three or more layers are used. 1861
See the rationale in 5.4.4.6.3. The procedure can be applied to both separable 1862 and non-separable layers as long as the material and material thickness is same 1863 for all the layers. 1864
5.4.4.6.5 Mandrel test 1865
Source: IEC 61558-1:2005, 26.3.3; IEC 60950-1:2013; IEC 60065:2011 1866
Purpose: This test should detect a break of the inner layer of non-separated foils. 1867
Rationale: This test procedure is taken from IEC 61558-1, 26.3.3, and the test voltage is 1868 150 % Utest, or 5 kV RMS., whatever is greater. 1869
5.4.4.7 Solid insulation in wound components 1870
Source: IEC 60950-1, IEC 61558-1 1871
Purpose: To identify constructional requirements of insulation of winding wires and 1872 insulation between windings. 1873
Rationale: Requirements have been used in IEC 60950-1 for many years and are aligned 1874 to IEC 61558-1. 1875
Planar transformers are not considered wound components and have to comply 1876 with G.13. 1877
5.4.4.9 Solid insulation requirements at frequencies higher than 30 kHz 1878
Source: IEC 60664-4:2005 1879
Purpose: To identify requirements for solid insulation that is exposed to voltages at 1880 frequencies above 30 kHz. 1881
Rationale: The requirements are taken from the data presented in Annex C of 1882 IEC 60664-4:2005. Testing of solid insulation can be performed at line 1883 frequency as detailed in 6.2 of IEC 60664-4:2005. 1884
– 57 – 108/757/DC
In general, the breakdown electric field strength of insulation can be determined 1885 according to IEC 60243-1 (Electrical strength of insulating materials−Test 1886 methods−Part 1) as referred from 5.3.2.2.1 of IEC 60664-1:2007 (see below). 1887 Note that this text is not repeated in IEC 60664-1:2020. 1888
5.3.2.2.1 Frequency of the voltage 1889
The electric strength is greatly influenced by the frequency of the applied 1890 voltage. Dielectric heating and the probability of thermal instability increase 1891 approximately in proportion to the frequency. The breakdown field strength of 1892 insulation having a thickness of 3 mm when measured at power frequency 1893 according to IEC 60243-1 is between 10 kV/mm and 40 kV/mm. Increasing the 1894 frequency will reduce the electric strength of most insulating materials. 1895
NOTE The influence of frequencies greater than 30 kHz on the electric strength is described in 1896 IEC 60664-4. 1897
Table 20 shows the electric field strength for some commonly used materials. 1898 These values are related to a frequency of 50/60 Hz. 1899
Table 21, which is based on Figure 6 of IEC 60664-4:2005, shows the reduction 1900 factor for the value of breakdown electric field strength at higher frequencies. 1901 The electric field strength of materials drops differently at higher frequencies. 1902 The reduction of the insulation property is to be considered when replacing the 1903 calculation method by the alternative ES test at mains frequency, as shown after 1904 the sixth paragraph of 5.4.4.9. Table 21 is for materials of 0,75 mm in thickness 1905 or more. Table 22 is for materials of less than 0,75 mm in thickness. 1906
The 1,2 times multiplier comes from IEC 60664-4:2005, subclause 7.5.1, where 1907 the partial discharge (PD) extinction voltage must include a safety margin of 1,2 1908 times the highest peak periodic voltage. 1909
5.4.5 Antenna terminal insulation 1910
Source: IEC 60065 1911
Purpose: To prevent breakdown of the insulation safeguard. 1912
Rationale: The insulation shall be able to withstand surges due to overvoltages present at 1913 the antenna terminals. These overvoltages are caused by electrostatic charge 1914 build up, but not from lightning effects. A maximum voltage of 10 kV is assumed. 1915 The associated test of G.10.4 simulates this situation by using a 10 kV test 1916 voltage discharged over a 1 nF capacitor. 1917
5.4.6 Insulation of internal wire as a part of a supplementary safeguard 1918
Source: IEC 60950-1 1919
Purpose: To specify constructional requirements of accessible internal wiring 1920
Rationale: Accessible internal wiring isolated from ES3 by basic insulation only needs a 1921 supplementary insulation. If the wiring is reliably routed away so that it will not 1922 be subject to handling by the ordinary person, then smaller than 0,4 mm thick 1923 supplementary insulation has been accepted in IEC 60950-1. But the 1924 insulation still has to have a certain minimum thickness together with electric 1925 strength withstand capability. The given values have been successfully used in 1926 products covered by this document for many years (see Figure 16 in this 1927 document). 1928
– 58 – 108/757/DC
1929
Figure 16 – Example illustrating accessible internal wiring 1930
5.4.7 Tests for semiconductor components and for cemented joints 1931
Source: IEC 60950-1 1932
Purpose: To simulate lifetime stresses on adjoining materials. 1933
To detect defects by applying elevated test voltages after sample conditioning. 1934
To avoid voids, gaps or cracks in the insulating material and delaminating in the 1935 case of multilayer printed boards. 1936
Rationale: This method has been successfully used for products in the scope of this 1937 document for many years. 1938
5.4.8 Humidity conditioning 1939
Source: IEC 60950-1 and IEC 60065. Alternative according to IEC 60664-1:2020, 6.4.3 1940
Purpose: Material preparations for dielectric strength test. Prerequisite for further testing. 1941
A tropical climate is a location where it is expected to have high temperatures 1942 and high humidity during most of the year. The document does not indicate what 1943 levels of temperature or humidity constitute a tropical climate. National 1944 authorities define whether their country requires products to comply with tropical 1945 requirements. Only a few countries, such as Singapore and China, have 1946 indicated in the CB scheme that they require such testing. 1947
5.4.9 Electric strength test 1948
Source: IEC 60664-1: 2020 1949
Purpose: To test the insulation to avoid breakdown. 1950
Rationale: Values of test voltages are derived from Table F.6 of IEC 60664-1:2020, however 1951 the test duration is 60 s. 1952
This method has been successfully used for products in the scope of IEC 60065 1953 and IEC 60950-1 for many years. 1954
– 59 – 108/757/DC The DC voltage test with a test voltage equal to the peak value of the AC voltage 1955
is not fully equivalent to the AC voltage test due to the different withstand 1956 characteristics of solid insulation for these types of voltages. However in case 1957 of a pure DC voltage stress, the DC voltage test is appropriate. To address this 1958 situation the DC test is made with both polarities. 1959
Table 25 Test voltages for electric strength tests based on transient voltages 1960
Source: IEC 60664-1:2020 1961
Rationale: To deal with withstand voltages and cover transients. 1962
The basic insulation and supplementary insulations are to withstand a test 1963 voltage that is equal to the transient peak voltage. The test voltage for the 1964 reinforced insulation shall be equal to the transient in the next in the preferred 1965 series. According to 5.2.5 of IEC 60664-1:2020, the use of 160 % test value for 1966 basic insulation as the test value for reinforced insulation is only applicable 1967 if other values than the preferred series are used. 1968
Functional insulation is not addressed, as is it presumed not to provide any 1969 protection against electric shock. 1970
Table 26 Test voltages for electric strength tests based on the peak of the working 1971 voltages and recurring peak voltages 1972
Source: IEC 60664-1:2020 1973
Rationale: Column B covers repetitive working voltages and requires higher test voltages 1974 due to the greater stress to the insulation. 1975
Recurring peak voltages (IEC 60664-1:2020, 5.4.3.2) need to be considered, 1976 when they are above the temporary overvoltage values, or in circuits separated 1977 from the mains. 1978
If the recurring peak voltages are above the temporary overvoltage values, 1979 these voltages have to be used, multiplied by the factor given in 1980 IEC 60664-1:2020, 5.4.3.2. 1981
Table 27 Test voltages for electric strength tests based on temporary overvoltages 1982
Source: IEC 60664-1:2020 1983
Rationale: Temporary overvoltages (IEC 60664-1:2020, 5.4.3.2) need to be considered as 1984 they may be present up to 5 s. The test voltage for reinforced insulation is 1985 twice the value of basic insulation. 1986
5.4.10 Safeguards against transient voltages from external circuits 1987
Source: IEC 62151:2000, Clause 6 1988
Purpose: To protect persons against contact with external circuits subjected to transients 1989 (for example, telecommunication networks). 1990
Rationale: External circuits are intended to connect the equipment to other equipment. 1991 Connections to remote equipment are made via communication networks, which 1992 could leave the building. Examples for such communication networks are 1993 telecommunication networks and Ethernet networks. The operating voltages of 1994 communication networks are usually within the limits of ES1 (for example, 1995 Ethernet) or within the limits of ES2 (for example, telecommunication networks). 1996
When leaving the buildings, communication networks may be subjected to 1997 transient overvoltages due to atmospheric discharges and faults in power 1998 distribution systems. These transients are depending on the infrastructure of the 1999 cables and are independent on the operating voltage of the communication 2000 network. The expected transients on telecommunication networks are specified 2001 in ITU-T recommendations. To avoid secondary hazards a separation between 2002 an external circuit connected to communication networks subjected transients 2003 is required. 2004
– 60 – 108/757/DC
Because the transient does not cause a hazardous electric shock the separation 2005 element needs not to be a reinforced safeguard nor a basic safeguard in the 2006 meaning of IEC 62368-1. It is sufficient to provide a separation complying with 2007 an electric strength test, only. Therefore for this separation no clearance, no 2008 creepage distances and no thickness requirements for solid insulation are 2009 required. 2010
The separation is required between the external circuit subjected to transients 2011 and all parts, which may accessible to ordinary persons or instructed 2012 persons. 2013
The likelihood a transient occurs and a body contact with an accessible part 2014 occurs at the same time increases with the contact time. Therefore non-2015 conductive parts and unearthed parts of the equipment maintained in continuous 2016 contact with the body during normal use (for example, a telephone handset, head 2017 set, palm rest surfaces) the separation should withstand a higher test voltage. 2018
Two test procedures for the electric strength test are specified in 5.4.10.2. 2019
5.4.10.2.2 Impulse test 2020
The impulse test is performing an impulse test by using the impulse generator 2021 for the 10/700 µs impulse (see test generator D.1 of Annex D). With the recorded 2022 waveforms it could be judged whether a breakdown of insulation has occurred, 2023 or if the surge suppression device has worked properly. 2024
The examples in Figure 17, Figure 18, Figure 19 and Figure 20 in this document 2025 could be used to assist in judging whether or not a surge suppressor has 2026 operated or insulation has broken down. 2027
2028
Consecutive impulses are identical in their waveforms.
2029
Figure 17 – Waveform on insulation without surge suppressors and no breakdown 2030
– 61 – 108/757/DC
Consecutive impulses are not identical in their waveforms. The pulse shape changes from pulse to pulse until a stable resistance path through the insulation is established. Breakdown can be seen clearly on the shape of the pulse voltage oscillogram.
2031
Figure 18 – Waveforms on insulation during breakdown without surge suppressors 2032
1 – gas discharge type
2 – semiconductor type
3 – metal oxide type
Consecutive impulses are identical in their waveforms.
Figure 19 – Waveforms on insulation with surge suppressors in operation 2033
2034
Figure 20 – Waveform on short-circuited surge suppressor and insulation 2035
– 62 – 108/757/DC 5.4.10.2.3 Steady-state test 2036
The steady-state test is performing an electric strength test according to 5.4.9.1. 2037 This test is simple test with an RMS voltage. But if for example, surge 2038 suppressors are used to reduce the transients from the external circuits within 2039 the equipment this RMS test may by not adequate. In this case an impulse test 2040 is more applicable. 2041
5.4.11 Separation between external circuits and earth 2042
Source: IEC 62151:2000, 5.3 2043
Purpose: To protect persons working on communication networks, and users of other 2044 equipment connected to the network from hazards in the equipment. 2045
Rationale: Class I equipment provides basic insulation between mains and earthed 2046 conductive parts and requires the conductive parts to be connected to a PE 2047 conductor that has to be connected to the earthing terminal in the buildings 2048 installation to be safe to use. In an isolated environment such an earth terminal 2049 is not present in the building installation. Nevertheless the use of class I 2050 equipment in such an isolated environment is still safe to use, because in case 2051 of a breakdown of the insulation in the equipment (fault of basic insulation) the 2052 second barrier is provided by the isolated environment (similar to a 2053 supplementary insulation). 2054
With the connection of the equipment via an external circuit to a communication 2055 network from outside the building installation to a remote environment the 2056 situation will change. It is unknown whether the remote environment is an 2057 isolated or non-isolated environment. During and after a fault of the basic 2058 insulation in a class I equipment (from mains to conductive parts) installed in 2059 an isolated installation (non-earthed installation) the conductive parts will 2060 become live (mains potential). If now the conductive parts are not separated 2061 from the external circuit, the mains voltage will be transferred to the remote 2062 installation via the communication network. This is a hazardous situation in the 2063 remote environment and can be dangerous for persons in that remote 2064 environment. 2065
Also in old building installations socket outlets exist with no earth contact. This 2066 situation will not be changed in the near future. 2067
To provide protection for those situations, a separation between an external 2068 circuit intended to be connected to communication networks outside the building 2069 (for example, telecommunication networks) and a separation between the 2070 external circuit and earthed parts is required. 2071
For this separation, it is sufficient to comply with the requirements of 5.4.11.2 2072 tested in accordance with 5.4.11.3. For this separation, no clearance, no 2073 creepage distances and no thickness requirements for solid insulation is 2074 required. 2075
5.5 Components as safeguards 2076
Rationale: For failure of a safeguard and a component or device that is not a safeguard: 2077
Safeguard failure: A failure is considered to be a safeguard failure if the part 2078 itself or its function, during normal operating conditions, contributes to change 2079 an ES class to a lower ES class. In this case, the part is assessed for its reliability 2080 by applying the applicable safeguard component requirements in 5.5 and the 2081 associated requirements in Annex G. When establishing ES1, ES2 limits apply 2082 during single fault condition of these parts. In case no requirements for the 2083 component are provided in 5.5 or Annex G, the failure is regarded as a non-2084 safeguard failure. 2085
– 63 – 108/757/DC Non-safeguard failure: A failure is considered to be a non-safeguard failure if 2086
the part itself or its function, under normal operating conditions, does not 2087 contribute to change an ES class to a lower ES Class. In this case, there is no 2088 need to assess the reliability of the part. When establishing ES1, ES1 limits apply 2089 for the single fault condition of these parts. Where applicable, 5.3.1 applies.2090 Figure 21 and Figure 22 in this document give practical examples of the 2091 requirements when ordinary components bridge insulation. 2092
Example 1 2093
2094
Figure 21 – Example for an ES2 source 2095
A single fault of any component or part may not result in the accessible part 2096 exceeding ES1 levels, unless the part complies with the requirements for a basic 2097 safeguard. 2098
The basic safeguard in parallel with the part(s) is to comply with: 2099
– the creepage distance requirements; and 2100
– the clearance requirements 2101
for basic insulation. 2102
There are no other requirements for the components or parts if the accessible 2103 part remains at ES1. 2104
Example 2 2105
2106
Figure 22 – Example for an ES3 source 2107
A single fault of any component or part may not result in the accessible part 2108 exceeding ES1 levels, unless the parts comply with the requirements for a 2109 double or reinforced safeguard. 2110
– 64 – 108/757/DC
The double safeguard or reinforced safeguard in parallel with the part(s) is to 2111 comply with: 2112
− the creepage distance requirements; and 2113
− the clearance requirements, 2114
for double insulation or reinforced insulation. 2115
There are no other requirements for the components or parts if the accessible 2116 part remains at ES1. 2117
5.5.2.1 General requirements 2118
Source: Relevant IEC component documents 2119
Purpose: The insulation of components has to be in compliance with the relevant insulation 2120 requirements of 5.4.1, or with the safety requirements of the relevant IEC 2121 document. 2122
Rationale: Safety requirements of a relevant document are accepted if they are adequate 2123 for their application, for example, Y2 capacitors of IEC 60384-14. 2124
5.5.2.2 Capacitor discharge after disconnection of a connector 2125
Source: IEC TS 61201:2007, Annex A 2126
Rationale: The 2 s delay time represents the typical access time after disconnecting a 2127 connector. When determining the accessible voltage 2 s after disconnecting a 2128 connector, the tolerance of the X capacitor is not considered. 2129
If a capacitor is discharged by a resistor (for example, a bleeder resistor), the 2130 correct value of the resistor can be calculated using the following formula: 2131
R = (2 / C) x [1 / ln(E / Emax)] MΩ 2132
where: 2133
C is in microfarads 2134
E is 60 for an ordinary person or 120 for an instructed person 2135
Emax is the maximum charge voltage or mains peak voltage 2136
ln is the natural logarithm function 2137
NOTE 1 When the mains is disconnected, the capacitance is comprised of both the X capacitors 2138 and the Y capacitors, and other possible capacitances. The circuit is analyzed to determine the 2139 total capacitance between the poles of the connector or plug. 2140
NOTE 2 If the equipment rated mains voltage is 125 V, the maximum value of the discharge 2141 resistor is given by: 2142
R = 1,85 / C MΩ 2143
NOTE 3 If the equipment rated mains voltage is 250 V, the maximum value of the discharge 2144 resistor is given by: 2145
R = 1,13 / C MΩ 2146
NOTE 4 The absolute value of the above calculations is used for the discharge resistor value. 2147
The test method includes a maximum time error of about 9% less than the 2148 calculated time for a capacitive discharge. This error was deemed acceptable for 2149 the sake of consistency with past practice. 2150
For measuring the worst case, care should be taken that the discharge is 2151 measured while at the peak of the input voltage. To ensure this, an automatic 2152 control system that switches off at the peak voltage can be used. 2153
– 65 – 108/757/DC
A method used by several other documents, such as IEC 60065 and IEC 60335-1 2154 is to repeat the measurement 10 times and record the maximum value. This 2155 assumes that one of the 10 measurements will be sufficiently close to the peak 2156 value. 2157
Another possibility might be to use an oscilloscope during the measurement, so 2158 one can see if the measurement was done near the maximum. 2159
Single fault conditions need not be considered if the component complies with 2160 the relevant component requirements of the document. For example, a resistor 2161 connected in parallel with a capacitor where a capacitor voltage becomes 2162 accessible upon disconnection of a connector, need not be faulted if the resistor 2163 complies with 5.5.6. 2164
When determining the accessible voltage 2 s after disconnection of the 2165 connector, the tolerance of the X-capacitor is not considered. 2166
5.5.6 Resistors 2167
Source: IEC 60950-1 and IEC 60065 2168
Rationale: When a group of resistors is used, the resistors are in series. The whole path 2169 consists of the metal lead and helical end (metal) and resistor body. The 2170 clearance and creepage distance is across the resistor body only. The total 2171 path then consists of conductive metal paths and resistor bodies (all in series). 2172 In this case, Figure O.4 becomes relevant when you want to determine the total 2173 clearance and creepage distance. 2174
5.5.7 SPDs 2175
Rationale: See Attachment A for background information on the use of SPD’s. 2176
It should be noted that the issue is still under discussion in IEC TC 108. The 2177 rationale will be adapted as soon as the discussion is finalized. 2178
A GDT is a gap, or a combination of gaps, in an enclosed discharge medium 2179 other than air at atmospheric pressure, and designed to protect apparatus or 2180 personnel, or both, from high transient voltages (from ITU-T K.12- 2181 Characteristics of gas discharge tubes for the protection of telecommunications 2182 installations). It shall be used to protect equipment from transient voltages. 2183
Even if a GDT operates during the occurrence of transient voltages, it is not 2184 hazardous according to 5.2.2.4, Electrical energy source ES1 and ES2 limits of 2185 Single pulses. 2186
NOTE These single pulses do not include transients. 2187
Because a transient does not cause a hazardous electric shock, the separation 2188 element does not need to be a reinforced safeguard nor a basic safeguard in 2189 the meaning of IEC 62368-1. 2190
If suitable components are connected in-series to the SPD (such as a VDR, etc.), 2191 a follow current will not occur, and there will be no harmful effect. 2192
5.5.8 Insulation between the mains and an external circuit consisting of a coaxial 2193 cable 2194
Source: IEC 60065:2014, 10.2 and IEC 60950-1:2005, 1.5.6. 2195
Rationale: The additional conditioning of G.10.2 comes from IEC 60950-1:2005, 1.5.6 2196 Capacitors bridging insulation. 2197
The 21-days of damp-heat conditioning of resistors serving as a safeguard 2198 between the mains and an external circuit consisting of a coaxial cable is 2199 necessary to ensure the reliability of such resistors. 2200
Except for components such as the resistors in parallel of the insulation between 2201 the mains and the connection to a coaxial cable, the 21-days of damp-heat 2202 conditioning is not necessary for this insulation in IEC 60065, IEC 60950-1 and 2203 IEC 62368-1. 2204
– 66 – 108/757/DC 5.6 Protective conductor 2205
See Figure 23 in this document for an overview of protective earthing and 2206 protective bonding conductors. 2207
2208
Figure 23 – Overview of protective conductors 2209
5.6.1 General 2210
Source: IEC 60364-5-54, IEC 61140, IEC 60950-1 2211
Purpose: The protective earthing should have no excessive resistance, sufficient 2212 current-carrying capacity and not be interrupted in all circumstances. 2213
5.6.2.2 Colour of insulation 2214
Source: IEC 60446 1 2215
Purpose: For clear identification of the earth connection. 2216
An earthing braid is a conductive material, usually copper, made up of three or 2217 more interlaced strands, typically in a diagonally overlapping pattern. 2218
It should be noted that IEC 60227-1:2007 has specific requirements for the use 2219 of the colour combination as follows: 2220
2221
2222
___________ 1 This publication was withdrawn.
– 67 – 108/757/DC 5.6.3 Requirements for protective earthing conductors 2223
Source: IEC 60950-1 2224
Purpose: The reinforced protective conductor has to be robust enough so that the 2225 interruption of the protective conductor is prevented in any case (interruption 2226 is not to be assumed). 2227
Rationale: These requirements have been successfully used for products in the scope of 2228 this document for many years. 2229
Where a conduit is used, if a cord or conductor exits the conduit and is not 2230 protected, then the values of Table 30 cannot be used for the conductor that 2231 exits the conduit. 2232
For pluggable equipment type B and permanently connected equipment, an 2233 earthing connection is always expected to be present. The earthing conductor 2234 can therefore be considered as a reinforced safeguard. 2235
5.6.4 Requirements for protective bonding conductors 2236
Source: IEC 60950-1 2237
Purpose: To demonstrate the fault current capability and the capability of the termination. 2238
Rationale: These requirements and tests have been successfully used for products in the 2239 scope of this document for many years (see Figure 3 in this document). 2240
5.6.5 Terminals for protective conductors 2241
5.6.5.1 Requirements 2242
Source: IEC 60998-1, IEC 60999-1, IEC 60999-2, IEC 60950-1 2243
Purpose: To demonstrate the fault current capability and the capability of the termination. 2244
Rationale: Conductor terminations according to Table 32 have served as reliable 2245 connection means for products complying with IEC 60950-1 for many years. 2246
The value of 25 A is chosen to cover the minimum protective current rating in all 2247 countries of the world. 2248
5.6.6.2 Test method 2249
Source: IEC 60950-1 2250
Rationale: This method has been successfully used for products in the scope of this 2251 document for many years. 2252
5.6.7 Reliable connection of a protective earthing conductor 2253
Source: IEC 60309 (plugs and socket outlets for industrial purpose) 2254
Purpose: To describe reliable earthing as provided by permanently connected 2255 equipment, pluggable equipment type B, and pluggable equipment type A. 2256
Rationale: Permanently connected equipment is considered to provide a reliable earth 2257 connection because it is wired by an electrician. 2258
Pluggable equipment type B is considered to provide a reliable earth 2259 connection because IEC 60309 type plugs are more reliable and earth is always 2260 present as it is wired by an electrician. 2261
For stationary pluggable equipment type A where a skilled person verifies 2262 the proper connection of the earth conductor. 2263
5.7 Prospective touch voltage, touch current and protective conductor current 2264
Source: IEC 60990 2265
– 68 – 108/757/DC 5.7.3 Equipment set-up, supply connections and earth connections 2266
Rationale: Equipment that is designed for multiple connections to the mains, where more 2267 than one connection is required, shall be subjected to either of the tests below: 2268
– have each connection tested individually while the other connections are 2269 disconnected, 2270
– have each connection tested while the other connections are connected, with 2271 the protective earthing conductors connected together. 2272
For simultaneous multiple connections, the requirement in the document is that 2273 each connection shall be tested while the other connections are connected, with 2274 the protective earthing conductors connected together. If the touch current 2275 exceeds the limit in 5.2.2.2, the touch current shall be measured individually. 2276
This means that if the total touch current with all connections tested together 2277 does not exceed the limit, the equipment complies with the requirement, if not, 2278 and each of the individual conductor touch currents don’t exceed the limit, the 2279 equipment also complies with the requirement. 2280
5.7.5 Earthed accessible conductive parts 2281
Rationale: Figure 24 in this document is an example of a typical test configuration for touch 2282 current from single phase equipment on star TN or TT systems. Other 2283 distribution systems can be found in IEC 60990. 2284
2285
Figure 24 – Example of a typical touch current measuring network 2286
5.7.6 Requirements when touch current exceeds ES2 limits 2287
Source: IEC 61140:2001, IEC 60950-1 2288
Rationale: The 5 % value has been used in IEC 60950-1 for a long time and is considered 2289 acceptable. The 5 % value is also the maximum allowed protective conductor 2290 current (7.5.2.2 of IEC 61140:2001). 2291
In the case that the protective conductor current exceeds 10 mA, IEC 61140 2292 requires a reinforced protective earthing conductor with a conductor size of 2293 10 mm2 copper or 16 mm2 aluminium or a second terminal for a second 2294 protective earthing conductor. This paragraph of IEC 62368-1 takes that into 2295 account by requiring a reinforced or double protective earthing conductor as 2296 per 5.6.3. 2297
– 69 – 108/757/DC IEC 61140:2001, 7.5.2.2 requires information about the value of the protective 2298
conductor current to be in the documentation and in the instruction manual, to 2299 facilitate the determination that the equipment with the high protective 2300 conductor current is compatible with the residual current device which may be 2301 in the building installation. 2302
The manufacturer shall indicate the value of the protective conductor current 2303 in the installation instructions if the current exceeds 10 mA, this to be in line with 2304 the requirements of IEC 61140:2001, 7.6.3.5. 2305
5.7.7 Prospective touch voltage and touch current associated with external circuits 2306
5.7.7.1 Touch current from coaxial cables 2307
Source: IEC 60728-11 2308
Purpose: To avoid having an unearthed screen of a coaxial network within a building. 2309
Rationale: An earthed screen of a coaxial network is reducing the risk to get an electric 2310 shock. 2311
Coaxial external interfaces very often are connected to antennas to receive TV 2312 and sound signals. Antennas installed outside the buildings are exposed to 2313 external atmospheric discharges (for example, indirect lightning). To protect the 2314 antenna system and the equipment connected to such antennas, a path to earth 2315 needs to be provided via the screen of the coaxial network. 2316
Each piece of mains-powered equipment delivers touch current to a coaxial 2317 external circuit via the stray capacitance and the capacitor (if provided) 2318 between mains and coaxial interface. This touch current is limited by the 2319 requirement for each individual equipment to comply with the touch current 2320 requirements (safe value) to be measured according IEC 60990. Within a 2321 building, much individual equipment (for example, TV’s receivers) may be 2322 connected to a coaxial network (for example, cable distribution system). In this 2323 case, the touch current from each individual equipment sums up in the shield 2324 of the coaxial cable. With an earthed shield of a coaxial cable, the touch current 2325 has a path back to the source and the shield of the coaxial cable remains safe 2326 to touch. 2327
5.7.7.2 Prospective touch voltage and touch current associated with paired 2328 conductor cables 2329
Source: IEC 62151 2330
Purpose: To avoid excessive prospective touch voltage and excessive currents from 2331 equipment into communication networks (for example, telecommunication 2332 networks). 2333
Rationale: All touch current measurements according to IEC 60990 measure the current 2334 from the mains to accessible parts. ES1 circuits are permitted to be accessible 2335 by an ordinary person and therefore it is included in the measurement 2336 according to IEC 60990. Circuits of class ES2 are not accessible and therefore 2337 these classes of circuits are not covered in the measurements according to 2338 IEC 60990. 2339
Because ES2 circuits may be accessible to instructed persons and may 2340 become accessible during a single fault to an ordinary person, the touch 2341 current to external circuit has to be limited, to protect people working on 2342 networks or on other equipment, which are connected to the external circuit via 2343 a network. 2344
An example for an external interface ID 1 of Table 13 is the connection to a 2345 telecommunication network. It is common for service personal of 2346 telecommunication networks and telecommunication equipment to make 2347 servicing under live conditions. Therefore, the telecommunication networks are 2348 operating with a voltage not exceeding energy class ES2. 2349
– 70 – 108/757/DC
The rationale to limit the touch current value to 0,25 mA (lower than ES2) has 2350 a practical background. Telecommunication equipment very often have more 2351 than one external circuit ID 1 of Table 13 (for example, connection to a 2352 telecommunication network). In such configurations a summation of the touch 2353 current may occur (see 5.7.7). With the limitation to 0,25 mA per each individual 2354 external circuit up to 20 external circuits could be connected together without 2355 any additional requirement. In 5.7.7 this value of 0,25 mA is assumed to be the 2356 touch current from a network to the equipment. 2357
5.7.8 Summation of touch currents from external circuits 2358
Source: IEC 60950-1 2359
Purpose: To avoid excessive touch currents when several external circuits are 2360 connected. 2361
Rationale: When limiting the touch current value to each individual external circuit (as 2362 required in 5.7.6.2), more circuits can be connected together before reaching the 2363 touch current limit. This allows better utilization of resources. 2364
Detailed information about touch currents from external circuits is given in 2365 Annex W of IEC 60950-1:2005. 2366
a) Touch current from external circuits 2367
There are two quite different mechanisms that determine the current through a 2368 human body that touches an external circuit, depending on whether or not the 2369 circuit is earthed. This distinction between earthed and unearthed (floating) 2370 circuits is not the same as between class I equipment and class II equipment. 2371 Floating circuits can exist in class I equipment and earthed circuits in class II 2372 equipment. Floating circuits are commonly, but not exclusively, used in 2373 telecommunication equipment and earthed circuits in data processing 2374 equipment, also not exclusively. 2375
In order to consider the worst case, it will be assumed in this annex that 2376 telecommunication networks are floating and that the AC mains supply and 2377 human bodies (skilled persons, instructed persons or ordinary persons) are 2378 earthed. It should be noted that a skilled person and an instructed person can 2379 touch some parts that are not accessible by an ordinary person. An "earthed" 2380 circuit means that the circuit is either directly earthed or in some way referenced 2381 to earth so that its potential with respect to earth is fixed. 2382
a.1) Floating circuits 2383
If the circuit is not earthed, the current (Ic) through the human body is "leakage" 2384
through stray or added capacitance (C) across the insulation in the mains 2385 transformer (see Figure 25 in this document). 2386
2387
Figure 25 – Touch current from a floating circuit 2388
– 71 – 108/757/DC
This current comes from a relatively high voltage, high impedance source, and 2389 its value is largely unaffected by the operating voltage on the external circuit. 2390 In this document, the body current (Ic) is limited by applying a test using the 2391
measuring instrument in Annex D of IEC 60950-1:2005, which roughly simulates 2392 a human body. 2393
a.2) Earthed circuits 2394
If the external circuit is earthed, the current through the human body (Iv) is due 2395
to the operating voltage (V) of the circuit, which is a source of low impedance 2396 compared with the body (see Figure 26 in this document). Any leakage current 2397 from the mains transformer (see a.1), will be conducted to earth and will not 2398 pass through the body. 2399
2400
Figure 26 – Touch current from an earthed circuit 2401
In this document, the body current (Iv) is limited by specifying maximum voltage 2402
values for the accessible circuit, which shall be an ES1 circuit or (with restricted 2403 accessibility) an ES2 circuit. 2404
b) Interconnection of several pieces of equipment 2405
It is a characteristic of information technology equipment, in particular in 2406 telecommunication applications, that many pieces of equipment may be 2407 connected to a single central equipment in a "star" topology. An example is 2408 telephone extensions or data terminals connected to a PABX, which may have 2409 tens or hundreds of ports. This example is used in the following description (see 2410 Figure 27 in this document). 2411
2412
Figure 27 – Summation of touch currents in a PABX 2413
– 72 – 108/757/DC
Each terminal equipment can deliver current to a human body touching the 2414 interconnecting circuit (I1, I2, etc.), added to any current coming from the PABX 2415
port circuitry. If several circuits are connected to a common point, their individual 2416 touch currents will add together, and this represents a possible risk to an 2417 earthed human body that touches the interconnection circuit. 2418
Various ways of avoiding this risk are considered in the following subclauses. 2419
b.1) Isolation 2420
Isolate all interconnection circuits from each other and from earth, and limit I1, 2421
I2, etc., as described in a.1. This implies either the use in the PABX of a separate 2422
power supply for each port, or the provision of an individual line (signal) 2423 transformer for each port. Such solutions may not be cost effective. 2424
b.2) Common return, isolated from earth 2425
Connect all interconnection circuits to a common return point that is isolated from 2426 earth. (Such connections to a common point may in any case be necessary for 2427 functional reasons.) In this case the total current from all interconnection circuits 2428 will pass through an earthed human body that touches either wire of any 2429 interconnection circuit. This current can only be limited by controlling the values 2430 I1, I2, .. In. In relation to the number of ports on the PABX. However, the value 2431
of the total current will probably be less than I1 + I2 +... + In due to harmonic and 2432
other effects. 2433
b.3) Common return, connected to protective earth 2434
Connect all interconnection circuits to a common return point and connect that 2435 point to protective earthing. The situation described in a.2) applies regardless 2436 of the number of ports. Since safety depends on the presence of the earth 2437 connection, it may be necessary to use high-integrity earthing arrangements, 2438 depending on the maximum value of the total current that could flow. 2439
5.8 Backfeed safeguard in battery backed up supplies 2440
Source: IEC 62040-1:2017, IEC 62368-1, UL 1778 5th edition 2441
Purpose: To establish requirements for certain battery backed up power supply systems 2442 that are an integral part of the equipment and that have the capability to backfeed 2443 to the mains of the equipment during stored energy mode. Examples include 2444 CATV network distribution supplies and any other integral supply commonly 2445 evaluated under this document with a battery backed option. 2446
Rationale: Principles of backfeed safeguard 2447
Battery backed up supplies store and generate hazardous energy. These 2448 energies may be present at the input terminals of the unit. 2449
A backfeed safeguard is intended to prevent ordinary persons, instructed 2450 persons or skilled persons from unforeseeable or unnecessary exposure to 2451 such hazards. 2452
A mechanical backfeed safeguard should meet a minimum air gap requirement. 2453 If not, the mechanical device (contacts) may be forced closed, and this will not 2454 be counted as a fault. The backfeed safeguard operates with any and all 2455 semiconductor devices in any single phase of the mains power path failed. 2456
A backfeed safeguard works under any normal operating condition. This 2457 should include any output load or input source condition deemed normal by the 2458 manufacturer; however, it is common practice to only test at full- and no-load 2459 conditions, unless analysis of the circuitry proves other conditions would be less 2460 favourable. The circuitry that controls the backfeed safeguard is intended to be 2461 single-fault tolerant. 2462
– 73 – 108/757/DC
A backfeed safeguard can accomplish this by disconnecting the mains supply 2463 wiring from the internal energy source, by disabling the inverter and removing 2464 the hazardous source(s) of energy, reducing the source to a safe level, or by 2465 placing a suitable safeguard between the ordinary person, instructed person 2466 or skilled person and the hazardous energy. ES1 is defined in the body of this 2467 document. The method of measurement is as follows: 2468
– For pluggable equipment, it is determined by opening all phases, neutral and 2469 ground. 2470
– For permanently connected equipment, the neutral and ground are not 2471 removed during the backfeed safeguard tests. 2472
Measurements are taken at the unit input connections across the phases, from 2473 phase to neutral and phase and neutral to ground, using the body impedance 2474 model as the measurement device. 2475
Air gap requirements for mechanical disconnect: 2476
An air gap is only required when the backfeed safeguard is mechanical in 2477 nature. The air gap is defined as the clearance distance. There are several 2478 elements to consider when determining the clearance requirement: 2479
– Under normal operation, the space between poles of phases must meet the 2480 requirements for basic insulation (see 5.4.2). 2481
– If the unit is operating on inverter, the source is considered to be a secondary 2482 supply, which is transient free (see 5.4.2). 2483
For a unit with floating outputs, opening all phases and the neutral using the 2484 required clearance for basic insulation is considered acceptable. If the output 2485 is grounded to the chassis, reinforced insulation or equivalent is required. 2486
Fault testing 2487
All backfeed safeguard control circuits are subjected to failure analysis and 2488 testing. 2489
Relays 2490
Relays in the mains path that are required to open for mechanical protection 2491 should be normally open when not energized. 2492
If the relay does not meet the required clearances, the shorting of either 2493 pole/contact may be considered as a single fault to simulate the welding of the 2494 contacts. The failure of a single relay contact may be sensed and the inverter 2495 disabled to prevent feedback. 2496
A relay used for mechanical protection shall be horsepower-rated or pass a 50-2497 cycle endurance test at 600 % of the normal switching current. 2498
Electronic protection 2499
Electronic protection for a backfeed safeguard is acceptable if the operation of 2500 the electronic protection device is sensed and the inverter is disabled if a fault 2501 is found. This is the same requirement as for a relay having less than the 2502 required air gap or clearance or is not relied upon entirely for mechanical 2503 protection. 2504
Mechanical protection 2505
Mechanical protection for a backfeed safeguard is acceptable if it prevents the 2506 user from accessing greater than ES1 and cannot be readily defeated without 2507 the use of tool. The voltage rating of the mechanical protection should be no 2508 less than the maximum out-of-phase voltage. 2509
Control circuitry 2510
The failure, open- or short-circuit, of any component of the backfeed safeguard 2511 circuitry may be analyzed to evaluate the effects on the proper operation of the 2512 backfeed safeguard. Testing may be done on all components where analysis 2513 of the results is arguable. 2514
– 74 – 108/757/DC
Components, such as resistors and inductors, are considered to fail open-circuit 2515 only. In general, capacitors may fail open or shorted. Solid-state devices 2516 typically fail short and then open. 2517
Microprocessor controls are considered to be acceptable if the circuit operates 2518 safely with any single control line open or shorted to control logic ground, or 2519 shorted to Vcc where such fault is likely to occur. Failure of the microprocessor 2520 can also be simulated by opening the Vcc pin or shorting the Vcc pin to ground. 2521
If the control circuitry is fully redundant, (for example, N + 1), failure analysis of 2522 individual components is not required if the failure of one circuit results in a fail-2523 safe mode of operation. 2524
_____________ 2525
6 Electrically-caused fire 2526
Rationale: Electrically-caused fire is due to conversion of electrical energy to thermal 2527 energy, where the thermal energy heats a fuel material to pyrolyze the solid into 2528 a flammable gas in the presence of oxygen. The resulting mixture is heated 2529 further to its ignition temperature which is followed by combustion of that fuel 2530 material. The resulting combustion, if exothermic or with additional thermal 2531 energy converted from the electrical source, can be sustained and subsequently 2532 ignite adjacent fuel materials that result in the spread of fire. 2533
The three-block model (see 0.7.2, Figure 6) for electrically (internally) caused 2534 fire addresses the separation of a potential ignition sources from combustible 2535 materials. In addition, it can also represent an ignited fuel and the safeguards 2536 interposed between ignited fuels and adjacent fuels or to fuels located outside 2537 the equipment. 2538
6.2 Classification of power sources (PS) and potential ignition sources (PIS) 2539
Rationale: The first step in the application of this clause is to determine which energy 2540 sources contain potential ignition sources requiring a safeguard. The power 2541 available to each circuit can first be evaluated to determine the energy available 2542 to a circuit. Then each point or component within a circuit can be tested to 2543 determine the power that would be available to a fault at that component. With 2544 this information each part of the component energy sources within the product 2545 can be classified as either a specific ignition source or a component within a 2546 power source. 2547
Throughout the clause, the term “reduce the likelihood of ignition” is used in 2548 place of the terms “prevent” or “eliminate”. 2549
6.2.2 Power source circuit classifications 2550
Source: IEC 60950-1, IEC 60065 2551
Rationale: These power source classifications begin with the lowest available energy 2552 necessary to initiate an electronic fire (PS1) and include an intermediate level 2553 (PS2) where ignition is possible but the spread of fire can be localized with 2554 effective material control or isolation safeguards. The highest energy level 2555 (PS3), assumes both ignition and a potential spread of fire beyond the ignition 2556 source. Criteria for safeguards will vary based on the type of power source that 2557 is providing power to the circuit. 2558
This power measurement and source classification are similar to LPS test 2559 requirements from IEC 60950-1 but are applied independently and the criteria 2560 limited to available power as opposed to in combination of criteria required in 2561 IEC 60950-1. 2562
All circuits and devices connected or intended to be connected as a load to each 2563 measured power source are classified as being part of that power source. This 2564 test method determines the maximum power available from a power source to 2565 any circuit connected to that power source. 2566
– 75 – 108/757/DC The identification of test points for determination of power source is at the 2567
discretion of the manufacturer. The most obvious are outputs of internal power 2568 supply circuits, connectors, ports and board to board connections. However, 2569 these measurements can be made anywhere within a circuit. 2570
When evaluating equipment (peripherals) connected via cables to an equipment 2571 port or via cable, the impedance of any connecting cable may be taken into 2572 account in the determination of the PS classification of a connected peripheral. 2573 Therefore, it is acceptable to make the measurement at the supply connector or 2574 after the cable on the accessory side. 2575
The location of the wattmeter is critical, as the total power available from the 2576 power source (not the power available to the fault) is measured during each fault 2577 condition. As some fault currents may be limited by a protective device, the time 2578 and current breaking characteristics of the protective device used is considered 2579 where it has an effect on the value measured. 2580
This test method assumes a single fault in either the power source or the load 2581 circuits of the circuit being classified. It assumes both: 2582
a) a fault within the circuit being classified, and 2583
b) any fault within the power source supplying power to the circuit being 2584 classified, 2585
each condition a) or b) being applied independently. 2586
The higher of the power measured is considered the PS circuit classification 2587 value. 2588
6.2.2.2 Power measurement for worst-case fault 2589
Rationale: This test method determines the maximum power available from a power source 2590 that is operating under normal operating conditions to any circuit connected to 2591 that power source, assuming any single fault condition within the circuit being 2592 classified. This power measurement assumes normal operating conditions are 2593 established before applying the single fault to any device or insulation in the 2594 load circuit to determine the maximum power available to a circuit during a fault. 2595
This is different for potential ignition source power measurements where the 2596 measured power available is that at the fault location. 2597
A value of 125 % was chosen to have some degree of certainty that the fuse will 2598 open after a certain amount of time. As such, the measured situation will not be 2599 a continuous situation. It was impossible to use the interruption characteristics 2600 of a fuse, since different types of interrupting devices have completely different 2601 interrupting characteristics. The value of 125 % is a compromise that should 2602 cover the majority of the situations. 2603
6.2.2.3 Power measurement for worst-case power source fault 2604
Rationale: This test method determines the maximum power available to a normal load from 2605 a power source assuming any single fault within the power source. A power 2606 source fault could result in an increase in power drawn by a normal operating 2607 load circuit. 2608
6.2.2.4 PS1 2609
Source: IEC 60065, IEC 60695, IEC 60950-1 2610
Rationale: A PS1 source is considered to have too little energy to cause ignition in electronic 2611 circuits and components. 2612
The requirement is that the continuous available power be less than 15 W to 2613 achieve a very low possibility of ignition. The value of 15 W has been used as 2614 the lower threshold for ignition in electronic components in many documents, 2615 including IEC 60950-1 and IEC 60065. It has also routinely been demonstrated 2616 through limited power fault testing in electronic circuits. 2617
– 76 – 108/757/DC
– In order to address the ease of measurement, it was decided to make the 2618 15 W measurement after 3 s. The value of 3 s was chosen to permit ease of 2619 measurement. Values as short as 100 ms and as high as 5 s were also 2620 considered. Quickly establishing a 15 W limit (less than 1 s) is not practical 2621 for test purposes and not considered important for typical fuel ignition. It is 2622 recognized that it normally takes as long as 10 s for thermoplastics to ignite 2623 when impinged directly by a small flame (IEC 60695 small scale material 2624 testing methods). 2625
– In principle the measurements are to be made periodically (for example, each 2626 second) throughout the 3 s period with the expectation that after 3 s, the 2627 power would “never” exceed 15 W. 2628
– Historically telecommunication circuits (Table 13, ID 1) are power limited by 2629 the building network to values less than 15 W and the circuits connected to 2630 them are considered PS1 (from IEC 60950-1). 2631
It should be noted that the statement for external circuits is not intended to 2632 cover technologies such as USB and PoE. It is meant to relate to analogue 2633 ringing signals only. 2634
6.2.2.5 PS2 2635
Source: IEC 60695-11-10, IEC 60950-1 2636
Rationale: Power Source 2 assumes a level of energy that has the possibility of ignition and 2637 subsequently requires a safeguard. Propagation of the ignition beyond the 2638 initially ignited component is limited by the low energy contribution to the fault 2639 and subsequently by safeguards to control the ignition resistance of nearby 2640 fuels. 2641
The primary requirement is to limit power available to these circuits to no more 2642 than 100 W. This value includes both power available for normal operation and 2643 the power available for any single fault condition. 2644
− This value has been used in IEC 60950-1 for a similar purpose, where ignition 2645 of internal components is possible but fire enclosures are not required. 2646
− The value of 100 W is commonly used in some building or fire codes to identify 2647 where low power wiring can be used outside of a fire containing enclosure. 2648
− The value is also 2 × 50 W, which can be related to the energy of standard 2649 flaming ignition sources (IEC 60695-11-10 test flame) on which our small-2650 scale V-rating material flammability classes are based. It is recognized that 2651 the conversion of electrical energy to thermal energy is far less than 100 %, 2652 so this value is compatible with the safeguards prescribed for PS2 circuits, 2653 which are generally isolation and V-rated fuels. 2654
The 5 s measurement for PS2 ensures the available power limits are both limited 2655 and practical for the purposes of measurement. The value is also used in 2656 IEC 60950 series as referenced above. No short-term limits are considered 2657 necessary, as possibility of ignition is presumed for components in these power 2658 limited circuits, recognizing that it generally takes 10 s or more for 2659 thermoplastics to pyrolyze and then ignite when impinged directly by a small 2660 50 W flame. 2661
Reliability of overcurrent devices (such as those found in IEC 60950 series) is 2662 not necessary as these circuits are used within or directly adjacent to the product 2663 (not widely distributed like IEC 60950-1 LPS circuits used for connection to 2664 building power). The reliability assessment for PS2 circuits that are intended to 2665 be distributed within the building wiring is addressed for external circuits later 2666 in this document. 2667
– 77 – 108/757/DC 6.2.2.6 PS3 2668
Rationale: PS3 circuits are circuits that are not otherwise classified as PS1 or PS2 circuits. 2669 No classification testing is required as these circuits can have unlimited power 2670 levels. If a circuit is not measured, it can be assumed to be PS3. 2671
6.2.3 Classification of potential ignition sources 2672
Rationale: With each power source, points and components within a circuit can be 2673 evaluated to determine if potential ignition sources are further identified. 2674 These ignition sources are classified as either an arcing PIS for arcing sources 2675 or a resistive PIS for resistance heating sources. Criteria for safeguards will 2676 vary based on the type of PIS being addressed. 2677
Ignition sources are classified on their ability to either arc or dissipate excessive 2678 heat (resistive). It is important to distinguish the type of ignition source as 2679 distances through air from arcing parts versus other resistive ignition sources 2680 vary due to a higher thermal loss in radiated energy as compared to conducted 2681 flame or resistive heat impinging directly on a combustible fuel material. 2682
6.2.3.1 Arcing PIS 2683
Source: IEC 60065 2684
Rationale: Arcing PIS are considered to represent a thermal energy source that results 2685 from the conversion of electrical energy to an arc, which may impinge directly or 2686 indirectly on a fuel material. 2687
Power levels below 15 W (PS1) are considered to be too low to initiate an 2688 electrical fire in electronic circuits. This value is used in IEC 60065 (see also 2689 6.2.1). 2690
The minimum voltage (50 V) required to initiate arcing is also from IEC 60065 2691 and through experimentation. 2692
For low-voltages, the fault that causes arc-heating is generally a result of a loose 2693 connection such as a broken solder connection, a cold-solder connection, a 2694 weakened connector contact, an improperly crimped wire, an insufficiently 2695 tightened screw connection, etc. As air does not break down below 300 V RMS. 2696 (Paschen’s Law), most low voltage arc-heating occurs in direct contact with a 2697 fuel. For voltages greater than 300 V, arcing can occur through air. 2698
The measurement of voltage and current necessary to establish an arcing PIS is 2699 related the energy that is available to the fault (as opposed to energy available 2700 from a power source). The value (Vp × Irms) specified is neither a W or VA but 2701 rather a calculated number reflecting a peak voltage and RMS current. It is not 2702 directly measurable. 2703
Arcing below 300 V is generally the result of a disconnection of current-carrying 2704 connections rather than the mating or connection of potentially current-carrying 2705 connections. 2706
Once the basic parameters of voltage and power are met, there are three 2707 conditions for which safeguards are required: 2708
− separation that can be created during a single fault, those that can arc under 2709 normal operating conditions; 2710
− all terminations where electrical failure resulting in heating is more likely; and 2711
− any electrical condition (such as the opening of a trace). 2712
A reliable connection is a connection which is expected not to become 2713 disconnected within the lifetime of the equipment. The examples in the note give 2714 an idea as to what kinds of connections can be considered reliable. 2715
The manufacturer may declare any location to be an arcing PIS. 2716
– 78 – 108/757/DC 6.2.3.2 Resistive PIS 2717
Source: IEC 60065 2718
Rationale: Resistive potential ignition sources can result from a fault that causes over-2719 heating of any impedance in a low-resistance that does not otherwise cause an 2720 overcurrent protection to operate. This can happen in any circuit where the 2721 power to the resistive heating source is greater than 15 W (see above). A 2722 resistive PIS may ignite a part due to excessive power dissipation or ignite 2723 adjacent materials and components. 2724
Under single fault conditions, this clause requires that two conditions exist 2725 before determining that a part can be a resistive PIS. The first is that there is 2726 sufficient available fault energy to the component. The second is that ignition of 2727 the part or adjacent materials can occur. 2728
The requirement for a resistive PIS under normal operating conditions is not 2729 the available power but rather the power dissipation of the part under normal 2730 operating conditions. 2731
The value of 30 s was used in IEC 60065 and has historically proven to be 2732 sufficient. The value of 100 W was used in IEC 60065 and has historically proven 2733 to be adequate. 2734
The manufacturer may declare any location to be a resistive PIS. 2735
6.3 Safeguards against fire under normal operating conditions and abnormal 2736 operating conditions 2737
Rationale: The basic safeguard under normal operating conditions and abnormal 2738 operating conditions is to reduce the likelihood of ignition by limiting 2739 temperature of fuels. This can be done by assuring that any available electrical 2740 energy conversion to thermal energy does not raise the temperature of any part 2741 beyond its ignition temperature. 2742
2743
Figure 28 – Possible safeguards against electrically-caused fire 2744
– 79 – 108/757/DC
There are several basic safeguards and supplementary safeguards against 2745 electrically-caused fire under abnormal operating conditions and single fault 2746 conditions (see Figure 28, Table 8 and Table 9 in this document). These 2747 safeguards include, but are not limited to: 2748
S1) having insufficient power to raise a fuel material to ignition temperature; 2749
S2) limiting the maximum continuous fault current; limiting the maximum duration for 2750 fault currents exceeding the maximum continuous fault current (for example, a 2751 fuse or similar automatic-disconnecting overcurrent device); 2752
S3) selecting component rating based on single fault conditions rather than 2753 normal operating conditions (prevents the component from overheating); 2754
S4) ensuring high thermal resistance of the thermal energy transfer path from the 2755 thermal energy source to the fuel material (reduces the temperature and the rate 2756 of energy transfer to the fuel material so that the fuel material cannot attain 2757 ignition temperature); or a barrier made of non-combustible material; 2758
S5) using an initial fuel material located closest to an arcing PIS or resistive PIS 2759 having a temperature rating exceeding the temperature of the source (prevents 2760 fuel ignition); or a flame-retardant fuel material (prevents sustained fuel burning 2761 and spread of fire within the equipment); or a non-combustible material (for 2762 example, metal or ceramic); 2763
S6) ensuring high thermal resistance of the thermal energy transfer path from the 2764 initial fuel to more fuel material; or flame isolation of the burning initial fuel from 2765 more fuel material (prevents spread of fire within the equipment); 2766
S7) ensuring that subsequent material is either non-combustible material (for 2767 example, metal or ceramic); or is a flame-retardant material (prevents sustained 2768 fuel burning and spread of fire within the equipment); 2769
S8) use of a fire-containing enclosure (contains the fire within the equipment) or 2770 an oxygen-regulating enclosure (quenches a fire by suffocating it); 2771
S9) use of reliable electrical connections; 2772
S10) use of non-reversible components and battery connections; 2773
S11) use of mechanical protection (for example, barriers, mesh or the like) with limited 2774 openings; 2775
S12) use of clear operating instructions, instructional safeguards, cautions. 2776
Methods of protection 2777
A) Protection under normal operating conditions and abnormal 2778 operating conditions 2779
Materials and components shall not exceed their auto-ignition temperatures. 2780
B) Protection under single fault conditions 2781
There are two methods of providing protection. Either method may be applied to 2782 different circuits in the same equipment: 2783
− Prevent ignition: equipment is so designed that under abnormal operating 2784 conditions and single fault conditions no part will ignite; 2785
− Control fire spread: selection and application of components, wiring, materials 2786 and constructional measures that reduce the spread of flame and, where 2787 necessary, by the use of a fire enclosure. 2788
Thermoplastic softening values or relative thermal indices (RTI) were not 2789 considered appropriate as they do not relate specifically to ignition properties of 2790 fuel materials. 2791
Any device that operates as a safeguard during normal operation (when left in 2792 the circuit) shall be assessed for reliability. If a device is taken out of the circuit 2793 during the normal operation testing then it is not considered as being a 2794 safeguard. 2795
– 80 – 108/757/DC
Abnormal operating conditions that do not result in a single fault are 2796 considered in much the same way as normal operating conditions as the 2797 condition is corrected and normal operation is presumed to be restored. 2798 However, abnormal operating conditions that result in a single fault 2799 condition are to be treated in accordance with 6.4 rather than 6.3. See Figure 29 2800 in this document for a fire clause flow chart. 2801
Table 8 – Examples of application of various safeguards 2802
Cause Prevention/protection methods Safeguard
Start of fire under normal operating conditions
Limit temperature of combustible material Basic
Start of fire under abnormal operating conditions and single fault conditions
Select prevent ignition or control fire spread method
Supplementary
PS1 circuit Low available power reduces the likelihood of ignition
S1
PS2 or PS3 circuit Reduce the likelihood of ignition
Use of protection devices
S1, S2, S3, S5
S2
Sufficient distance or solid barrier interposed between any combustible material and each potential ignition source
S4 (S6)
PS2 circuit Limit the available power
Sufficient distance or solid barrier interposed between any combustible material and each potential ignition source
Use flame-retardant or non-combustible material
S1, S2
S4, S6
S5
PS3 circuit Use all PS2 options and:
− use fire containing enclosures
− use flame-retardant or similar materials
S8
S7
Internal and external wiring Reliable construction
Limit of wire temperature and use of fire resistant insulation
S9
Fire caused by entry of foreign objects and subsequent bridging of electrical terminals in PS2 circuits and PS3 circuits
Prevent entry of foreign objects S11
Mains supply cords Reliable construction
Limit of wire temperature and use of fire resistant insulation
S9
Fire or explosion due to abnormal operating conditions of batteries
Limit charge/discharge currents
Limit short-circuit currents
Prevent use of wrong polarity
S1
S2
S10
2803
– 81 – 108/757/DC
2804
Figure 29 – Fire clause flow chart 2805
6.3.1 Requirements 2806
Source: IEC 60950-1, ISO 871 2807
Rationale: Spontaneous-ignition temperature as measured by ISO 871 for materials was 2808 chosen as the ignition point of fuels. The materials specific tables were deleted 2809 in favour of a simple requirement or completely referring to the ASTM standard 2810 for material auto-ignition temperatures. 2811
– 82 – 108/757/DC The 300 °C value for thermoplastics is approximately 10 % less than the lowest 2812
ignition temperature of materials commonly used in ICT and CE equipment. This 2813 value has also been used in IEC 60950-1. The designer is permitted to use 2814 material data sheets for materials that exceed this value but the auto-ignition 2815 specification has to be reduced by 10 % to accommodate measurement 2816 variations and uncertainty. 2817
In the context of fire, abnormal operating conditions (blocked vents, connector 2818 overload, etc.) are to be considered just as a normal operating condition 2819 unless the abnormal operating condition results in a single fault condition. 2820
As part of the compliance check, first the datasheets of the materials used have 2821 to be checked to be able to evaluate the results of the temperature rise 2822 measurements. 2823
The glow-wire test is a fire test method of applying a heat source to the sample. 2824 The test provides a way to compare a material’s tendency to resist ignition, self-2825 extinguish flames (if ignition occurs), and to not propagate fire. Manufacturers 2826 have been using this test method to determine a plastic’s flame resistance 2827 characteristics to IEC 60950-1 for many years without field issues identified with 2828 the suitability of the test. Hence, the glow-wire test should continue to be an 2829 option to the HB rating for plastics outside of the fire enclosure or mechanical 2830 enclosures and for electrical enclosures housing PS1 circuits. This 2831 precedence has been set in IEC 60950-1 and should be included in IEC 62368-2832 1. 2833
Table 9 – Basic safeguards against fire under normal operating conditions 2834 and abnormal operating conditions 2835
Normal operating conditions and abnormal operating conditions
The objective of this subclause is to define requirements to reduce the likelihood of ignition under normal operating conditions and abnormal operating conditions.
PS1
PS2
PS3 6.3.1
Ignition is not allowed
Tmax ≤ 90 % auto ignition temperature according to ISO 871; or Tmax ≤ 300 ºC
Combustible materials for components and other parts outside fire enclosures (including electrical enclosures, mechanical enclosures and decorative parts), shall have a material flammability class of at least: – HB75 if the thinnest significant thickness of this material is < 3 mm, or – HB40 if the thinnest significant thickness of this material is ≥ 3 mm, or – HBF.
NOTE Where an enclosure also serves as a fire enclosure, the requirements for fire enclosures apply.
These requirements do not apply to: – parts with a size of less than 1 750 mm3; – supplies, consumable materials, media and recording materials; – parts that are required to have particular properties in order to perform
intended functions, such as synthetic rubber rollers and ink tubes; – gears, cams, belts, bearings and other parts that would contribute
negligible fuel to a fire, including labels, mounting feet, key caps, knobs and the like.
2836
6.3.2 Compliance criteria 2837
Rationale: Steady state for temperature measurements in excess of 300 °C requires more 2838 tolerance on the rise value due to the difficulty in achieving a stable reading. 2839 However, the value in B.1.6 was considered adequate, as these values typically 2840 do not continue to rise but rather cycle. The value of 3 °C over a 15 min period 2841 was also considered for measurement of these very high temperatures but was 2842 not used in favour of harmonization with other clauses. 2843
– 83 – 108/757/DC The use of temperature-limiting safeguards under normal operating 2844
conditions and abnormal operating conditions is considered acceptable only 2845 where the safeguard or device has been deemed a reliable temperature control 2846 device. 2847
6.4 Safeguards against fire under single fault conditions 2848
6.4.1 General 2849
Source: IEC 60065, IEC 60950-1 2850
Rationale: The consideration in the prior clause is to limit the likelihood of 2851 ignition of fuels under normal operating conditions and abnormal operating 2852 conditions with a basic safeguard. All fuels should be used below their ignition 2853 temperatures and separated from arcing parts. 2854
The requirements in this clause are to limit the ignition or the spread of fire under 2855 single fault conditions by employing supplementary safeguards, see 2856 Table 10 in this document. There are two approaches that can be used either 2857 jointly or independently: 2858
− method 1 minimizes the possibility of ignition through the use of safeguards 2859 applied at each potential point of ignition; 2860
− method 2 assumes the ignition of limited fuels within the product and therefore 2861 requires safeguards that limit the spread of fire beyond the initial ignition 2862 point or for higher energy, beyond the equipment enclosure. 2863
Table 10 – Supplementary safeguards against fire under single fault conditions 2864
Single fault conditions
There are two methods of providing protection. Either method may be applied to different circuits of the same equipment (6.4.1)
Method 1
Reduce the likelihood of
ignition
Equipment is so designed that under single fault conditions no part shall ignite.
This method can be used for any circuit in which the available steady state power to the circuit does not exceed 4 000 W.
The appropriate requirements and tests are detailed in 6.4.2 and 6.4.3.
Method 2
Control fire spread
Selection and application of supplementary safeguards for components, wiring, materials and constructional measures that reduce the spread of fire and, where necessary, by the use of a second supplementary safeguard such as a fire enclosure.
This method can be used for any type of equipment.
The appropriate requirements are detailed in 6.4.4, 6.4.5 and 6.4.6.
2865
The document’s user or product designer will select a method to apply to each 2866 circuit, (either prevent ignition method or control the spread of fire method). The 2867 selection of a method can be done for a complete product, a part of a product or 2868 a circuit. 2869
The power level of 4 000 W was chosen to ensure that products which are 2870 connected to low power mains (less than 240 V × 16 A), common in the office 2871 place or the home, could use the ignition protection methods, and to provide a 2872 reasonable and practical separation of product types. It is recognized that this is 2873 not representative of fault currents available but is a convenient and 2874 representative separation based on equipment connected to normal office and 2875 home mains circuits where experience with potential ignition sources 2876 safeguards is more common. 2877
– 84 – 108/757/DC Limit values below 4 000 W create a problem for the AC mains of almost all 2878
equipment used in the home or office, which is not the intent. It would be much 2879 more practical to use an energy source power of 4 000 W based on mains 2880 voltage and overcurrent device rating which would effectively permit all 2881 pluggable type A equipment to use either method, and restrict very high-power 2882 energy sources to use only the method to control fire spread. 2883
The 4 000 W value can be tested for individual circuits; however, a note has 2884 been added to clarify which types of products are considered below without test. 2885 Calculation of the product of the mains nominal voltage and mains overcurrent 2886 device rating is not a normal engineering convention but rather the product of 2887 two numbers should not exceed 4 000 (see text below). 2888
NOTE All pluggable equipment type A are considered to be below the steady state value of 2889 4 000 W. Pluggable equipment type B and permanently connected equipment are considered 2890 to be below this steady state value if the product of nominal mains voltage and the current rating 2891 of the installation overcurrent protective device is less than 4 000. 2892
Prevent ignition method: Prescribes safeguard requirements that would prevent 2893 ignition and is predominantly based on fault testing and component selection and 2894 designs that reduce the likelihood of sustained flaming. Where a PIS is identified, 2895 additional safeguards are required to use barriers and the fire cone ‘keep out’ 2896 areas for non-flame rated materials (see Table 11 and Figure 30 in this 2897 document). 2898
The prevent ignition method has been used in IEC 60065 where the predominant 2899 product connection is to low power (< 16 A) mains circuits. The use of this 2900 method was not considered adequate enough for larger mains circuits because 2901 the size of the fire cone does not adequately address large ignition sources 2902 common in higher power circuits. 2903
This approach limits the use of prevent ignition methods to those products where 2904 the ignition sources is characterized by the fire cones and single fault 2905 conditions described in 6.4.7. 2906
– 85 – 108/757/DC
Table 11 – Method 1: Reduce the likelihood of ignition 2907
Method 1: Reduce the likelihood of ignition under single fault conditions
PS1
(≤ 15 W after 3) 6.4.2 No supplementary safeguards are needed for protection against PS1.
A PS1 is not considered to contain enough energy to result in materials reaching ignition temperatures.
PS2
( > PS1 and
≤ 100 W after 5 s)
and
PS3
(> PS2 and
≤ 4 000 W)
6.4.3
The objective of this subclause is to define the supplementary safeguards needed to reduce the likelihood of ignition under single fault conditions in PS2 circuits and PS3 circuits where the available power does not exceed 4 000 W. All identified supplementary safeguards need to be considered based on the equipment configuration.
Sustained flaming > 10 s is not allowed and no surrounding parts shall have ignited.
Separation from arcing PIS and resistive PIS according to 6.4.7
– Distances have to comply with Figures 37, 38, 39a and 39b; or
– In case the distance between a PIS and combustible material is less than specified in Figures 37, 38, 39a and 39b;
• Mass of combustible material < 4 g, or
• Shielded from the PIS by a fire barrier, or
• Flammability requirements:
o V-1 class material; VTM-1 class material or HF-1 class material, or needle flame in Clause S.2, or
o Relevant component IEC document
Using protective devices that comply with G.3.1, G.3.2, G.3.3 and G.3.4 or the relevant IEC component documents for such devices;
Using components that comply with G.5.3, G.5.4 or the relevant IEC component document;
Components associated with the mains shall comply with:
the relevant IEC component documents; and
the requirements of other clauses of IEC 62368-1
2908
2909
– 86 – 108/757/DC
2910
Figure 30 – Prevent ignition flow chart 2911
– 87 – 108/757/DC
Control fire spread method: Prescribes safeguards that are related to the spread 2912 of fire from acknowledged ignition sources. This assumes very little performance 2913 testing (no single fault conditions) and the safeguards are designed to 2914 minimize the spread of flame both within the product and beyond the fire 2915 enclosure. The safeguards described are based on power level, with higher 2916 power sources requiring more substantial safeguards (see Figure 31, Figure 32 2917 and Table 12 in this document). 2918
This power (4 000 W) separation is also used in the control of fire spread method 2919 to delineate safeguard criteria for fire enclosure materials (V-1 versus 5 V). 2920 IEC 60950-1 has historically used weight to define fire enclosure criteria and it 2921 was felt that the use of available power was more appropriate and generally 2922 reflective of current practice. 2923
2924
2925
2926
Figure 31 – Control fire spread summary 2927
– 88 – 108/757/DC
2928
Figure 32 – Control fire spread PS2 2929
2930
– 89 – 108/757/DC
2931
Figure 33 – Control fire spread PS3 2932
– 90 – 108/757/DC
6.4.2 Reduction of the likelihood of ignition under single fault conditions in PS1 2933 circuits 2934
Rationale: Low available power prevents ignition – 15 W is recognized as the lower limit of 2935 ignition for electronic products. The limiting of power is not considered the basic 2936 safeguard but rather the characteristic of the circuit being considered. This 2937 determination is made as part of the classification of power sources. 2938
6.4.3 Reduction of the likelihood of ignition under single fault conditions in PS2 2939 circuits and PS3 circuits 2940
Rationale: To identify all potential ignition sources, all circuits and components within the 2941 PS2 and PS3 circuits should be evaluated for their propensity to ignite. 2942
The ignition source derived from either PS2 or a PS3 circuit is considered 2943 equivalent. The resulting flame size and burn time is identical in all PS2 and PS3 2944 circuits unless the power available is very large (for example, greater than 2945 4 000 W). 2946
For very large sources (greater than 4 000 W) the safeguards described for 2947 addressing potential ignition sources are not recognized as being adequate 2948 and the control fire spread method is used (see 6.4.1 for 4 000 W rationale). 2949
6.4.3.1 Requirements 2950
Source: IEC 60065, IEC 60695-2-13, IEC 60950-1 2951
Rationale: Flaming of a fuel under single fault conditions is only permitted if very small 2952 and quickly extinguished (for example, a fuse resistor). A length of time is 2953 necessary during single fault conditions to permit the characteristic “spark” or 2954 short term “combustion flash” common when performing single fault conditions 2955 in electronic circuits. The value of 10 s is used, which has been used by 2956 IEC 60065 for many years. The energy of this short-term event is considered too 2957 low to ignite other parts. This value corresponds with IEC 60695-2-13 and has 2958 been used in practice by IEC TC 89 for glow wire ignition times. The time period 2959 is necessary to accommodate the expected flash/short duration flames that often 2960 result as a consequence of faults. The value of 10 s is considered to be the 2961 minimum time needed for ignition of commonly used thermoplastics by direct 2962 flame impingement. It is recognized that times as short as 2 s are used by other 2963 documents. 2964
Protection is achieved by identifying each PIS and then limiting the temperature 2965 of parts below auto-ignition temperatures during single fault conditions, 2966 minimizing the amount of flammable material near a PIS, separating 2967 combustible materials from PIS by barriers, and by using reliable protection 2968 devices to limit temperature of combustible parts. 2969
Single fault testing, while not statistically significant, has been common practice 2970 in both IEC 60065 and IEC 60950-1. 2971
Temperatures limiting ignition are considered to be the material self-ignition 2972 points or flash temperatures for flammable liquids and vapours (this value should 2973 include a 10 % margin to take into account ambient, laboratory and equipment 2974 operating conditions). The spread to surrounding parts during and after the fault 2975 is also checked. 2976
Providing sufficient distance or solid barrier between any combustible material 2977 and a potential ignition source should minimize the potential for the spread of 2978 fire beyond the fuels directly in contact with the potential ignition source. The 2979 fire cone distances developed for IEC 60065 are used and considered adequate. 2980 Single fault testing is not completely representative; therefore, some material 2981 and construction requirements are necessary (fuel control area or keep out 2982 area). 2983
Use of reliable protection devices – This includes reliability requirements for the 2984 devices that are used to prevent ignition. This permits only the use of devices 2985 that have reliability requirements included in Annex G. 2986
– 91 – 108/757/DC Components that comply with their relevant IEC component standards are also 2987
considered to comply given these standards also have ignition protection 2988 requirements. The components included are those that are almost always part 2989 of a potential ignition source as they are mains connected. 2990
Opening of a conductor: In general, opening of a conductor is not permitted 2991 during single fault conditions as it is not considered reliable protection device 2992 for limiting ignition. However for resistive PIS, it may be suitable provided the 2993 printed wiring board is adequately flame retardant and the opening does not 2994 create an arcing PIS. The V-1 printed circuit board is considered adequate to 2995 quench low voltage events and will not propagate the flame. It is not sufficient 2996 when the opening creates an arcing PIS (< 50 V). 2997
As a consequence of the test, any peeling of conductor during these tests shall 2998 not result in or create other hazards associated with the movement of conductive 2999 traces during or after the test provided they do so predictably. During a single 3000 fault the peeling could bridge a basic safeguard but should not result in the 3001 failure of a supplementary safeguard or reinforced safeguard. 3002
6.4.3.2 Test method 3003
Source: IEC 60065, IEC 60127 3004
Rationale: The available power and the classification criteria for resistive and arcing 3005 potential ignition sources should be used to determine which components to 3006 fault. 3007
If the applied single fault condition causes another device or subsequent fault, 3008 then the consequential failure is proven reliable by repeating the single fault 3009 condition two more times (total of three times). This is a method used 3010 historically in IEC 60065. 3011
Steady state determination for single fault conditions is related to temperature 3012 rise and the requirement is the same as the steady state requirements of Annex 3013 B, even though material ignition temperatures (> 300 °C) are much higher than 3014 required temperatures of other clauses (~25 °C – 100 °C). Shorter time periods 3015 (such as 15 min) were considered but dropped in favour of harmonization of 3016 other parts. The term steady state should take into account temperatures 3017 experienced by a material throughout the test. 3018
Maximum attained temperature for surrounding material of heat source should 3019 be considered if further temperature increase is observed after interruption of 3020 the current. 3021
Limit by fusing: The reliability of protection devices is ensured where they act 3022 to limit temperatures and component failures. The criteria used by the 3023 component document applying to each are considered adequate provided the 3024 parts are used as intended. The requirements included assume an IEC 60127 3025 type fuse as the most common device. 3026
The test methodology is established to ensure that available energy through the 3027 fuse link based on its current hold and interrupt conditions the breaking time 3028 characteristics of specified in IEC 60127. IEC 60127 permits 2,1 times the 3029 breaking current rating for 1 min. 3030
In order to determine the impact of a fuse on the results of a single fault 3031 condition, if a fuse operates, it is replaced with a short circuit and the test 3032 repeated. There are three possible conditions when comparing the actual fault 3033 current through the fuse to the pre-arcing current and time data sheets provided 3034 by the fuse manufacturer. 3035
– Where the measured current is always below the fuse manufacturer's pre-3036 arcing characteristics (measured current is less than 2,1 times the fuse 3037 rating), the fuse cannot be relied upon as a safeguard and the test is 3038 continued with the fuse short circuited until steady state where the maximum 3039 temperature is measured. 3040
– 92 – 108/757/DC
− Where the measured current quickly exceeds the fuse pre-arcing 3041 characteristics (measured current is well above 2,1 times the rating current of 3042 the fuse) then the test is repeated with the open circuit in place of the fuse 3043 (assumes fuse will open quickly and be an open circuit) and then the 3044 maximum temperature recorded. 3045
− Where the measured current does not initially exceed the fuse pre-arcing 3046 characteristics, but does at some time after introduction of the fault. The test 3047 is repeated with the short circuit in place and the temperature measured at 3048 the time where measured current exceeds the fuse pre-arcing characteristics. 3049 It is assumed the measured current through the short circuit can be graphed 3050 and compared with the fuse manufacturer’s pre-arcing curves provided on the 3051 fuse datasheet to determine the test time. 3052
6.4.4 Control of fire spread in PS1 circuits 3053
Rationale: Low available power reduces the likelihood for ignition – 15 W is recognized as 3054 the lower limit of ignition for electronic circuits. This lower power limit is 3055 considered as a circuit characteristic of the circuit, not a basic safeguard. 3056
– 93 – 108/757/DC
Table 12 – Method 2: Control fire spread 3057
Method 2: Control fire spread
PS1
(≤ 15 W) 6.4.4
No supplementary safeguards are needed for protection against PS1.
A PS1 is not considered to contain enough energy to result in materials reaching ignition temperatures.
PS2
(≤ 100 W after 5 s) 6.4.5
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS2 circuits to nearby combustible materials.
The limiting of power available to PS2 circuits is the basic safeguard used to minimize the available energy of an ignition source.
A supplementary safeguard is required to control the spread of fire from any possible PIS to other parts of the equipment
For conductors and devices with a PIS the following apply:
– Printed boards shall be at least V-1 class material
– Wire insulation shall comply with IEC 60332 series or IEC 60695-11-21
Battery cells and battery packs shall comply with Annex M.
All other components:
– Mounted on V-1 class material, or
– Materials V-2 class material, VTM-2 class material, or HF-2 class material, or
– Mass of combustible material < 4 g, provided that when the part is ignited the fire does not spread to another part, or
– Separated from PIS according to 6.4.7,
Distances have to comply with Figures 37; 38; 39 and 40, or
In case distances do not comply with Figures 37; 38; 39 and 40
– Mass of combustible material < 4 g, or
– Shielded from the PIS by a fire barrier, or
– Flammability requirements: V-1 class material; VTM-1 class material or HF-1 class material, or comply with the needle flame test of IEC 60695-11-5 as described in Clause S.2; or
– Comply with IEC component document flammability requirements, or comply with G.5.3 and G.5.4
– Insulation materials used in transformers, bobbins, V-1 class material
– In a sealed enclosure ≤ 0,06 m3 made of non-combustible material and having no ventilation openings
The following shall be separated from a PIS according to 6.4.7 or shall not ignite due to fault conditional testing
– Supplies, consumables, media and recording materials
– Parts which are required to have particular properties in order to perform intended functions, such as synthetic rubber rollers and ink tubes
3058
– 94 – 108/757/DC
Method 2: Control fire spread
PS3
(> PS2)
The objective of this subclause is to describe the supplementary safeguards needed to reduce the likelihood of fire spread from a PIS in PS3 circuits to nearby combustible materials.
6.4.6
Fire spread in PS3 circuit shall be controlled by;
– the use of a fire enclosure as specified in 6.4.8. and
– applying all requirements for PS2 circuits as specified in 6.4.5
Devices subject to arcing or changing contact resistance (for example, pluggable connectors) shall comply with one of the following:
– Materials V-1 class material; or
– Comply with IEC component document flammability requirements; or
– Mounted on V-1 class material and volume ≤ 1 750 mm3
Exemptions:
– Wire and tubing insulation complying with IEC 60332 series or IEC 60695-11-21
– Components, including connectors complying with 6.4.8.2.2 and that fill an opening in a fire enclosure
– Plugs and connectors forming a part of a power supply cord or complying with 6.5, G.4.1 and G.7
– Transformers complying with G.5.3
– Motors complying with G.5.4
6.4.6
For PS2 or a PS3 circuit
within a fire en-closure
See all requirements for PS2 (6.4.5)
6.4.6
For a PS1 circuit
within a fire
enclosure
Combustible materials:
Needle flame test in Clause S.1 or V-2 class material or VTM-2 class material or HF-2 class material
Exemptions:
– Parts with a size less than 1 750 mm3
– Supplies, consumable materials, media and recording materials
– Parts that are required to have particular properties in order to perform intended functions such as synthetic rubber rollers and ink tubes
– Gears, cams, belts, bearings and other small parts that would contribute negligible fuel to a fire, including, labels, mounting feet, key caps, knobs and the like
– Tubing for air or any fluid systems, containers for powders or liquids and foamed plastic parts, provided that they are of HB75 class material if the thinnest significant thickness of the material is < 3 mm, or HB40 class material if the thinnest significant thickness of the material is ≥ 3 mm, or HBF class foamed material
3059
6.4.5 Control of fire spread in PS2 circuits 3060
Source: IEC 60950-1 3061
Rationale: In principle, limiting the available power to the circuit (100 W) in PS2 circuits and 3062 control of adjacent fuel materials will reduce the spread of fire, assuming that 3063 ignition of components can occur. This power level limit minimizes the size of 3064 the ignition source and its impingement on adjacent fuels that are in the PS2 3065 circuits. 3066
– 95 – 108/757/DC The purpose of this clause is to establish control of fuels in or near circuits that 3067
have the possibility of ignition. As no fault testing is done for PS2 circuits, it is 3068 assumed that a fire ignition can occur anywhere within the circuits. These 3069 safeguards are to be based on component material flammability characteristics 3070 that keep the initial ignition source from spreading to surrounding internal 3071 materials. 3072
This clause assumes only construction safeguards in a manner consistent with 3073 the historically effective requirements of IEC 60950-1. 3074
Only fuels that would contribute significant fuel to a fire are considered. 3075
Acceptance of limited power sources in Annex Q.1 to be classified as PS2 has 3076 been added to allow continued use of the long existing practice in IEC 60950-1. 3077
6.4.5.2 Requirements 3078
Source: IEC 60065, IEC 60950-1 3079
Rationale: Requirements around conductors and devices subject to arcing parts and 3080 resistive heating have the most onerous requirements for sustained ignition and 3081 protection of wiring and wiring boards. 3082
− Mounting on a flame-retardant material to limit fire growth. V-1 mounting 3083 materials are considered important as they limit fuel to reduce sustained 3084 flaming and also would not contribute to large fires or pool fire. The spread of 3085 fire from ignited small parts can be managed by the larger printed wiring 3086 board. This provision is made to allow the use of a longstanding IEC 60950-1 3087 provision for small devices mounted directly on boards. The value 1 750 mm3 3088 has been used in practice in IEC 60065. 3089
− Use of flame retardant wiring is identical to the internal and external wiring 3090 requirements of Clause 6. 3091
− Accepting existing component requirements for devices that have their own 3092 requirements (IEC or annexes of this document) are considered adequate. 3093
− Sufficient distance or solid flame-resistant barrier between any combustible 3094 material and potential ignition sources. (KEEP OUT ZONES or 3095 RESTRICTED AREA). 3096
All other components (those that are not directly associated with arcing or 3097 resistive heating components) have a reduced set of safeguards when 3098 compared to those parts more likely to ignite. Those safeguards include any of 3099 the following: 3100
− For parts not directly subject to arcing or resistive heating, V-2 ratings are 3101 considered adequate. This is also a historical requirement of IEC 60950-1 for 3102 parts used in limited power circuits. Sustained ignition of V-2 class materials 3103 is similar to that of V-1 class materials in the small-scale testing. The use of 3104 VTM-2 or HF-2 class materials were also considered adequate. 3105
− Limiting the combustible fuel mass within the area around PS2 circuit 3106 devices. The limit of 4 g is brought from the small parts definition used with 3107 PIS requirements of this clause and which were originally used in IEC 60065. 3108
− As an alternative, components and circuits can be separated from fuels per 3109 the requirements of the fire cone described for isolation of fuels from 3110 potential ignition sources. 3111
− Enclosing parts in small oxygen limiting, flame proof, housing. The 0,06 m2 3112 value has been in practice in IEC 60950-1 and small enough to mitigate fire 3113 growth from a low power source. 3114
– 96 – 108/757/DC
The exceptions included are based on common constructions of material that do 3115 not routinely have flame retardants or that cannot contain flame retardants due 3116 to functional reasons. They are either isolated from any PIS or through single 3117 fault condition testing demonstrate that they will simply not ignite in their 3118 application. 3119
Supplies are quantities of materials such as paper, ink, toner, staples etc., and 3120 that are consumed by the equipment and replaced by the user when necessary. 3121
6.4.5.3 Compliance criteria 3122
Rationale: Material flammability requirements are checked by the testing of Annex S, by 3123 compliance with the component document or through review of material data 3124 sheets. 3125
6.4.6 Control of fire spread in a PS3 circuit 3126
Source: IEC 60950-1 3127
Rationale: There are two basic requirements to control the spread of fire from PS3 circuits: 3128
a) use of materials within the fire enclosure that limit fire spread. This includes 3129 the same requirements as for components in PS2 circuits and includes a 3130 requirement from IEC 60950-1 to address all combustible materials that are 3131 found within the fire enclosure; 3132
b) use fire-containing enclosures – Product enclosures will have a design 3133 capable of preventing the spread of fire from PS3 circuits. The criteria for 3134 fire enclosures is based on the available power. 3135
Rationale: PS3 sourced circuits may contain a significant amount of energy. During single 3136 fault conditions, the available power may overwhelm the safeguard of material 3137 control of fuels adjacent to the fault or any consequential ignition source making 3138 a fire enclosure necessary as part of the supplementary safeguard. A fire 3139 enclosure and the material controls constitute the necessary supplementary 3140 safeguard required for a PS3 circuit. 3141
Use adequate materials, typically permitting material pre-selection of non-3142 combustible or flame-resistant materials for printed wiring and components in 3143 or near PS3. Only fuels that would contribute significant fuel to a fire are 3144 considered. This implies compliance with all the requirements for PS2 circuits 3145 and in addition, application of a fire containing enclosure. 3146
Material flammability requirements for all materials inside a fire enclosure are 3147 included in this clause. This model has been used historically in IEC 60950-1 to 3148 control the amount and type of fuel that may become engaged in a significant 3149 fire. Because there is no single fault testing when applying this method, a 3150 significant ignition source may engage other fuels located inside the fire 3151 enclosure. PS3 circuits, particularly higher power PS3 circuits can create 3152 significant internal fires if adjacent combustible materials, not directly 3153 associated with a circuit, become involved in an internal fire. These fires, if 3154 unmitigated, can overwhelm the fire enclosures permitted in this document. 3155 Control of material flammability of fuels located within the enclosure should be 3156 sufficient based on historical experience with IEC 60950-1. 3157
The exceptions provided in this clause for small parts, consumable material, 3158 etc. that are inside of a fire enclosure, mechanical components that cannot 3159 have flame retardant properties are exempt from the material flammability 3160 requirements. This is the current practice in IEC 60950-1. 3161
Components filling openings in a fire enclosure that are also V-1 are considered 3162 adequate, as it is impractical to further enclose these devices. These 3163 constructions are commonly used today in IT and CE products. 3164
Wiring already has requirements in a separate part of this clause. 3165
Motors and transformers have their own flammability spread requirements and 3166 as such do not need a separate enclosure (see G.5.3 and G.5.4). 3167
– 97 – 108/757/DC 6.4.7 Separation of combustible materials from a PIS 3168
Rationale: Where potential ignition sources are identified through classification and 3169 single fault conditions, separation from the ignition source by distance 3170 (material controls) or separation by barriers are used to limit the spread of fire 3171 from the ignition source and are necessary to ensure the ignition is not 3172 sustained. 3173
6.4.7.2 Separation by distance 3174
Source: IEC 60065 3175
Rationale: The safeguard for materials within the fire cone includes material size control 3176 (and including prohibition on co-location of flammable parts). Otherwise the 3177 parts close to the PIS shall be material flammability class V-1, which limits 3178 sustained ignition and spread. 3179
Small parts (less than 4 g) are considered too small to significantly propagate a 3180 fire. This value is also used for components used in PS2 and PS3 circuits. It has 3181 been used in IEC 60065 with good experience. 3182
Where these distances are not maintained, a needle flame test option is included 3183 with 60 s needle flame application based on previous requirements in 3184 IEC 60065. This alternative to these distance requirements (the needle flame 3185 test) can be performed on the barrier to ensure that any additional holes resulting 3186 from the test flame are still compliant (openings that will limit the spread of fire 3187 through the barrier). 3188
Redundant connections: An arcing PIS cannot exist where there are redundant 3189 or reliable connections as these connections are considered not to break or 3190 separate (thereby resulting in an arc). 3191
Redundant connections are any kind of two or more connections in parallel, 3192 where in the event of the failure of one connection, the remaining connections 3193 are still capable of handling the full power. Arcing is not considered to exist 3194 where the connections are redundant or otherwise deemed not likely to change 3195 contact resistance over time or through use. Some examples are given, but proof 3196 of reliable connections is left to the manufacturer and there is no specific criteria 3197 that can be given: 3198
− Tubular rivets or eyelets that are additionally soldered – this assumes that the 3199 riveting maintains adequate contact resistance and the soldering is done to 3200 create a separate conductive path. 3201
− Flexible terminals, such as flexible wiring or crimped device leads that 3202 remove mechanical stress (due to heating or use) from the solder joint 3203 between the lead and the printed wiring trace. 3204
− Machine or tool made crimp or wire wrap connections – well-formed 3205 mechanical crimps or wraps are not considered to loosen. 3206
− Printed boards soldered by auto-soldering machines and the auto-soldering 3207 machines have two solder baths, but they are not considered reliable without 3208 further evaluation. This means most printed boards have been subjected to a 3209 resoldering process. But there was no good connection of the lead of the 3210 component(s) and the trace of the printed board in some cases. In such cases, 3211 resoldering done by a worker by hand may be accepted. 3212
Combustible materials, other than V-1 printed wiring boards are to be 3213 separated from each PIS by a distance based on the size of resulting ignition of 3214 the PIS. The flame cone dimensions 50 mm and 13 mm dimensions were derived 3215 from IEC 60065, where they have been used for several years with good 3216 experience. The area inside the cone is considered the area in which an open 3217 flame can exist and where material controls should be applied. 3218
– 98 – 108/757/DC
Resistive potential ignition sources are never a point object as presented in 3219 Figure 37 of IEC 62368-1. They are more generally three-dimensional 3220 components, however only one dimension and two-dimension drawings are 3221 provided. The three-dimensional drawing is difficult to understand and difficult to 3222 make accurate. 3223
Figure 34 in this document shows how to cope with potential ignition sources 3224 that are 3D volumes. This drawing does not include the bottom part of the fire 3225 cone. The same approach should be used for the bottom side of the part. 3226
Figure 34 – Fire cone application to a large component
The fire cone is placed at each corner. The locus of the outside lines connecting 3227 each fire cone at both the top and the base defines the restricted volume. 3228
Figure 37 Minimum separation requirements from a PIS 3229
This drawing of a flame cone and its dimensions represents the one-dimension 3230 point ignition source drawn in two dimensions. The three-dimension envelope 3231 (inverted ice cream cone) of a flame from a potential ignition source. This PIS 3232 is represented as a point source in the drawing for clarity, however these PISs 3233 are more often three-dimensional components that include conductors and the 3234 device packaging. 3235
Figure 38 Extended separation requirements from a PIS 3236
A two-dimensional representation of an ignition source intended to provide more 3237 clarity. 3238
6.4.7.3 Separation by a fire barrier 3239
Source: IEC 60065 3240
Rationale: The use of flame retardant printed wiring is considered necessary as the fuel 3241 and the electrical energy source are always in direct contact. V-1 has historically 3242 been adequate for this purpose. 3243
Printed wiring boards generally directly support arcing PIS and as such, cannot 3244 be used as a barrier. There is a potential that small openings or holes may 3245 develop, thus permitting the arc to cross through the board. 3246
A printed board can act as a barrier for an arcing PIS, provided the PIS is not 3247 directly mounted on the board acting as a barrier. 3248
– 99 – 108/757/DC
For resistive PIS, printed wiring boards can be used provided they are of V-1 or 3249 meet the test of Clause S.1. Any V-1 and less-flammable fuels are required to 3250 minimize the possibility flammable material falling onto the supporting surface 3251 or contact with combustible fuels (resulting in pool fires). If a PIS is located on 3252 a board and supplied by a PS2 or PS3 source, there should be no other PS2 or 3253 PS3 circuits near the PIS, as this could create faults due to PIS heating that was 3254 not otherwise considered. 3255
Figure 39 Deflected separation requirements from a PIS when a fire barrier is used 3256
This figure demonstrates the change on the fire cone when there is a fire barrier 3257 used to separate combustible material from a potential ignition source. This 3258 drawing was retained as an example application for only two angles. Recognizing 3259 that many examples are possible, only two are kept for practical reasons. History 3260 with multiple drawings of barriers in varying angles could be difficult to resolve. 3261 The fire team decided to keep only two drawings with an angle barrier as 3262 representative. 3263
6.4.8 Fire enclosures and fire barriers 3264
Rationale: The safeguard function of the fire enclosure and the fire barrier is to impede 3265 the spread of fire through the enclosure or barrier (see Table 13 in this 3266 document). 3267
– 100 – 108/757/DC
Table 13 – Fire barrier and fire enclosure flammability requirements 3268
Flammability requirements
Fire barrier
6.4.8.2.1
Fire barrier requirements Non-combustible material or Needle flame test Clause S.1 or ≥ V-1 class material or VTM-1 class material
6.4.8.4
Separation of a PIS to a fire barrier – Distance ≥ 13 mm to an arcing PIS and
– Distance ≥ 5 mm to a resistive PIS Smaller distances are allowed provided that the part of the fire barrier complies with one of the following: – Needle flame Clause S.2; After the test no holes bigger than in 6.4.8.3.3
and 6.4.8.3.4 allowed or
– ≥ V-0 class material
Fire enclosure
6.4.8.2.2
Fire enclosure materials: – Non-combustible, or – For PS3 ≤ 4 000 W, needle flame test Clause S.1 or V-1 class material – For PS3 > 4 000 W, needle flame test Clause S.5 or 5VB class material
Component materials which fill an opening in a fire enclosure or intended to be mounted in such opening – Comply with flammability requirements of relevant IEC component
document; or – ≥ V-1 class material; or – needle flame test Clause S.1
6.4.8.4
Separation of a PIS to a fire enclosure – Distance ≥ 13 mm to an arcing PIS and
– Distance ≥ 5 mm to a resistive PIS Smaller distances are allowed, provided that the part of the fire enclosure complies with one of the following: – Needle flame Clause S.2; After the test no holes bigger than in 6.4.8.3.3
and 6.4.8.3.4 allowed; or – ≥ V-0 class material
3269
6.4.8.2.1 Requirements for a fire barrier 3270
Source: IEC 60065, IEC 60950-1 3271
Rationale: Barriers used to separate PIS from flammable fuels reduce the ability of a 3272 resulting PIS flame from impinging on flammable materials. This can be achieved 3273 by using flame retardant materials that pass the performance test in Clause S.1 3274 or the pre-selection criteria of a minimum V-1 flame class. 3275
The test in Clause S.1 is based on the needle flame test which is currently an 3276 option for enclosure testing in both IEC 60950-1 and IEC 60065. 3277
6.4.8.2.2 Requirements for a fire enclosure 3278
Source: IEC 60065, IEC 60950-1 3279
Rationale: The material flammability class V-1 was chosen as the minimum value based 3280 on its historical adequacy, and recent testing done during the development of 3281 the requirements for externally caused fire. 3282
IEC 60950-1 – Prior requirements for 5 V class materials based on product 3283 weight lacked sufficient rationale. This has been improved and related to power 3284 available to a fault in this document. 3285
– 101 – 108/757/DC IEC 60065 – V-2 class material performance during large scale test reviewed 3286
by the fire team indicated inconsistencies in performance over a range of 3287 different V-2 materials. The propensity for V-2 class materials to create ‘pool’ 3288 fires is also detrimental to fire enclosure performance and therefore not 3289 accepted unless it passes the end-product testing. 3290
In addition to pre-selection requirements, an end-product test (material test) is 3291 also included by reference to Clauses S.1 (for < 4 000 W) and S.5 (for > 3292 4 000 W). This test is based on the needle flame test which is currently an option 3293 for enclosure testing in both IEC 60950-1 and IEC 60065. 3294
This power (4 000 W) separation is also used in the control of fire spread method 3295 to delineate safeguard criteria for fire enclosure materials (V-1 versus 5 V). 3296 IEC 60950-1 has historically used weight to define fire enclosure criteria and it 3297 was felt the use of available power was more appropriate and generally reflective 3298 of current practice. 3299
Both 5 VA and 5 VB class materials are considered acceptable for equipment 3300 with power above 4 000 W. This is consistent with current practice in IEC 60950-3301 1. 3302
6.4.8.2.3 Compliance criteria 3303
Rationale: In each case there is a performance test, and construction (pre-selection) criteria 3304 given. For material flammability, compliance of the material is checked at the 3305 minimum thickness used as a fire enclosure or fire barrier. 3306
6.4.8.3 Constructional requirements for a fire enclosure and a fire barrier 3307
Rationale: Opening requirements for barriers and fire enclosure should limit the spread of 3308 flame through any existing opening. A fire enclosure limits the spread of fire 3309 beyond the equipment and is permitted to have holes (within established limits). 3310
6.4.8.3.1 Fire enclosure and fire barrier openings 3311
Rationale: These requirements are intended to reduce the spread of an internal fuel ignition 3312 through a fire enclosure or barrier. 3313
Openings are restricted based on the location of each potential ignition source 3314 using the flame cones or in the case of control fire spread, above all PS3 circuits. 3315
Figure 40 Determination of top, bottom and side openings 3316
In the left figure, when the vertical surface has an inclination (angle) of less than 3317 5° from vertical, then only the side opening requirements of 6.4.8.3.5 apply. 3318
In the right figure, when the vertical surface has an inclination (angle) of more 3319 than 5° from the vertical, then the openings are subject to the requirements for 3320 top openings of 6.4.8.3.3 or bottom openings of 6.4.8.3.4. 3321
6.4.8.3.2 Fire barrier dimensions 3322
Rationale: Edges can be more easily ignited than a solid surface. Barrier dimensions shall 3323 also be sufficient to prevent ignition of the barrier edges. 3324
Barriers made of combustible materials shall have edges that extend beyond 3325 the limits of the fire cone associated with each potential ignition source. If the 3326 barrier edge does not extend beyond the cone, then it is assumed the edges 3327 may ignite. 3328
6.4.8.3.3 Top openings and top opening properties 3329
Source: IEC 60065 3330
Rationale: Top opening drawings are restricted in the areas of likely flame propagation to 3331 the side and above an ignition source. 3332
– 102 – 108/757/DC Top openings are also considered to cover what has historically been called side 3333
opening where the opening is above the horizontal plane containing the ignition 3334 source. 3335
The top/side openings that are subject to controls are only those within the fire 3336 cone drawing (Figure 37) plus a tolerance of 2 mm, as shown in Figure 41. The 3337 application of the fire cone dimensions has been used in IEC 60065 and proven 3338 historically adequate. 3339
Control of openings above the flame cone is also not necessary given that the 3340 heat transfer (convection) will follow the gases moving through those openings 3341 and is not sufficient to ignite adjacent materials. If the openings are directly 3342 blocked, the convection path will be blocked which would restrict any heat 3343 transfer to an object blocking the opening. 3344
Openings to the side of the fire cone dimensions were reviewed and ultimately 3345 not considered necessary as the radiant heat propagation through openings to 3346 the side of the ignition is very small. This radiant heat is not considered sufficient 3347 to ignite adjacent materials given the anticipated flame size and duration in AV 3348 and ICT products. 3349
In this aspect, the virtual flame cone deflection as per Figure 39 need not be 3350 considered since the actual needle flame application will cover that. 3351
The test method option proposed provides a test option for direct application of 3352 a needle flame. The test (S.2) referred to in this clause is intended to provide a 3353 test option where holes do not comply with the prescriptive measures. S.2 is 3354 originally intended to test the material flammability, but in this subclause the 3355 purpose of the test is to see the potential ignition of outer material covering the 3356 openings, so application of the needle flame is considered for that aspect rather 3357 than the burning property of the enclosure itself. 3358
Cheesecloth is used as a target material for the evaluation of flame spread due 3359 to its flexible nature (ease of use) and its quick propensity to ignite. 3360
The flame cone envelope is provided as a single point source. The applicable 3361 shape and any affecting airflow are taken into account for determining the whole 3362 shape of the PIS, not just a single point. The point is applied from the top edge 3363 of the component being considered and, in practice, it is rarely a single point. 3364
The opening dimensions for the 5 mm and 1 mm dimensions have been 3365 determined through test as being restrictive enough to cool combustible gases 3366 as they pass through the openings and those mitigate any flame from passing 3367 through the opening. Top openings properties are based on tests conducted by 3368 the fire team with open flames (alcohol in a Petri dish) that demonstrated these 3369 opening dimensions are adequate. 3370
6.4.8.3.4 Bottom openings and bottom opening properties 3371
Source: IEC 60065, IEC 60950-1 3372
Rationale: The location of openings is restricted for barriers inside the flame cone of 3373 Figure 37 and for enclosures, inside the cone and directly below to protect 3374 against flammable drips from burning thermoplastic as shown in Figure 42. The 3375 application of the fire cone dimensions has been used in IEC 60065 and proven 3376 historically adequate. 3377
There are several options for opening compliance (see Table 14 in this 3378 document). Flaming oils and varnishes are not common in ICT equipment today. 3379 The performance test based on the hot flaming oil test, in use for IEC 60950-1, 3380 have other opening options and are developed based on lower viscosity 3381 materials (when burning). They are more commonly found in ICT (that provide 3382 additional options). 3383
Clause S.3 (hot flaming oil test) is the base performance option and provides a 3384 test option (hot flaming oil test) that historically has been adequate for tests of 3385 bottom openings. 3386
– 103 – 108/757/DC The values in items band c) come directly from IEC 60950-1 where they have 3387
been historically adequate and have demonstrated compliance with the S.3 3388 performance testing. These requirements, previously from IEC 60950-1, 4.6.2 3389 Bottoms of fire enclosures, have been updated in the third edition of 3390 IEC 62368-1. The IEC 60950-1 requirements are more stringent than the new 3391 IEC 62368-1 requirements and may still be used as an option without additional 3392 tests, which is likely since designs based on the IEC 60950-1 requirements have 3393 been in use for some time. 3394
The work done to validate top openings was also considered adequate for bottom 3395 openings under materials of any properties (3 mm and 1 mm slots). This 3396 requirement is less onerous than those found in IEC 60950-1 which permitted 3397 NO openings unless they complied with the other options. 3398
Openings under V-1 class materials (or those that comply with Clause S.1) are 3399 controlled in the same manner as done in IEC 60950-1 which was considered 3400 adequate however an additional option to use 2 mm slots of unlimited length is 3401 also considered adequate. 3402
The 6 mm maximum dimension relates to a maximum square opening dimension 3403 of 36 mm2 and a round opening of 29 mm2. In IEC 60950-1 the requirement was 3404 40 mm2, which relates to a maximum 7 mm diameter if round or 6,3 mm 3405 maximum if not round. 3406
The only option where flammable liquids are used is to meet the requirements of 3407 the hot flaming oil test (Clause S.3). 3408
An option for equipment that is installed in special environments where a non-3409 combustible flooring is used (environmental safeguard) may obviate the need 3410 for an equipment bottom safeguard. This is current practice in IEC 60950-1 3411 where equipment is used in “restricted access locations”. 3412
Baffle plate constructions were added, as they have been used in IEC 60950-1 3413 and have proven to be an acceptable solution. 3414
The intent of IEC 62368-1 is to apply hazard-based safety engineering principles. 3415 When the calculated enclosure side opening size (when the 5-degree trajectory 3416 is applied) meets the maximum opening size permitted in both subclause 3417 6.4.8.3.4 and Annex P.2, it technically meets the requirements. Additionally, the 3418 flaming oil and entry of foreign object experimental testing done by the TC108 3419 HBSDT fire enclosure team demonstrated such safeguards provide suitable 3420 protection. Refer to Appendix A below for more details on testing. 3421
For side openings, refer to Figures 44 and 45 for illustration examples of using 3422 enclosure wall thickness in relationship to the vertical height of an opening to 3423 help determine if opening sizes meet requirements of 1) subclause 6.4.8.3.4 3424 (bottom fire enclosure openings); and 2) Annex P.2 (side opening requirement 3425 limitations to prevent vertical falling objects). 3426
– 104 – 108/757/DC
Table 14 – Summary – Fire enclosure and fire barrier material requirements 3427
Parameters Fire barrier Fire enclosure
Input < 4 000 W Input > 4 000 W
Com
bust
ible
mat
eria
l: Separation from PIS
13 mm or more from arcing PIS 5 mm or more from resistive PIS Note: exceptions may apply
Dimensions Sufficient to prevent ignition of the edges Not applicable
Flammability a) Test S.1; or b) V-1; or c) VTM-1
a) Test S.1; or b) V-1
a) Test S.5; or b) 5 VA; or c) 5 VB
Non
-C
ombu
stib
le
mat
eria
l:
Acceptable
Top openings See 6.4.8.3.3
Bottom openings See 6.4.8.3.4
3428
6.4.8.3.5 Side opening and side opening properties 3429
Source: IEC 60950-1 3430
Rationale: For Edition 3, IEC TC 108/WG HBSDT agreed to adopt from IEC 60950-1:2005 3431 (4.6.1, 4.6.2 and Figure 4E) the principles and criteria for determination of 3432 suitable side openings using a five (5) degree projection. The primary rationale 3433 for adopting these principles was the demonstration of many years of a solid 3434 safety record of use for ITE with IEC 60950-1. However, one issue that had to 3435 be resolved was that in IEC 60950-1 the 5-degree projection of Figure 4E was 3436 always made from the outer surface of a combustible internal component or 3437 assembly rather than a defined potential ignition source (PIS), typically a 3438 metallic circuit inside the component. The PIS principle was not inherent to 3439 IEC 60950-1. 3440
For example, in a component or assembly, electrical or not, made of combustible 3441 material that might ignite within a fire enclosure, the 5-degree projection was 3442 made from the surface of the component or assembly closest to the side 3443 enclosure and not from a metallic circuit inside the component or subassembly 3444 that could be a potential source of ignition. Therefore, for example, if a printed 3445 board was considered the component/subassembly likely to ignite, the 5-degree 3446 projection was made from the edge of the printed board and not the current 3447 carrying trace, which in IEC 62368-1 is the PIS. In some cases throughout the 3448 history of IEC 60950-1, this distance from the metallic trace to component edge 3449 could have been up to several centimetres. 3450
However, when IEC TC 108/WG HBSDT considered the common construction 3451 of internal components and subassemblies likely to be associated with a PIS, 3452 including printed boards, it was determined that it was reasonable to assume 3453 that in modern AV/ICT equipment the distance between the PIS and the outer 3454 edge of a component or sub-assembly was likely to have negligible impact on 3455 the overall fire safety of the product, in particular in the application of the 5 3456 degree principle. Due to general miniaturization of products, material cost 3457 optimization, and modern design techniques (including CAD/CAM), printed 3458 boards and other electronic components and assemblies associated with a PIS 3459 typically do not use unnecessary amounts of combustible materials – modern 3460 printed boards more typically now have metallic traces very close to the board 3461 edge rather than many millimetres away. 3462
– 105 – 108/757/DC
As a result IEC TC 108/WG HBSDT considered that the IEC 60950-1 five (5) 3463 degree projection principle for side openings remained sound even if projected 3464 from the actual PIS rather than the edge of combustible material associated with 3465 the PIS. This view also is consistent with the Note to Figure 38, Extended 3466 separation requirements from a PIS, which states, for a resistive PIS 3467 “…measurements are made from the nearest power dissipating element of the 3468 component involved. If in practice it is not readily possible to define the power 3469 dissipating part, then the outer surface of the component is used.” 3470
6.4.8.3.6 Integrity of a fire enclosure 3471
Source: IEC 60950-1 3472
Rationale: The clause ensures that a fire enclosure where required, is assured to remain 3473 in place and with the product through either an equipment or behavioural 3474 safeguard. This requirement is a service condition safeguard for ordinary 3475 persons to ensure that a fire enclosure (if required) is replaced prior to placing 3476 the equipment back into use. This safeguard is also required in IEC 60950-1. 3477
6.4.8.3.7 Compliance criteria 3478
Rationale: In each case, there is a performance test, and construction (pre-selection) 3479 criteria given. 3480
6.4.8.4 Separation of a PIS from a fire enclosure and a fire barrier 3481
Source: IEC 60065, IEC 60950-1 3482
Rationale: Non-metallic fire enclosures and fire barriers may not be sufficient to limit the 3483 spread of fire where an enclosure is close or in direct contact with a potential 3484 ignition source. 3485
The 13 mm and 5 mm distances were used in IEC 60065 to prevent an ignition 3486 source from transferring sufficient energy to adjacent flame-retardant V-1 3487 barriers. These distances are intended to reduce the likelihood of melting or 3488 burn-through of the barrier of fire enclosure. 3489
Where these distances are not maintained, a needle flame test option is included 3490 with 60 s needle flame application based on work in IEC 60065. 3491
Openings following the needle flame test were discussed with criteria being: 3492
a) no additional opening, 3493
b) no enlargement of existing holes, 3494
c) compliance with the fire enclosure opening requirements. 3495
Due to test repeatability, the criteria of a) are considered most readily 3496 reproduced. 3497
The option to use V-0 or 5 V class materials without distance or thickness 3498 requirements is based on historical practices in IEC 60065 and IEC 60950-1 3499 where no distance requirements were applied. 3500
The material thickness requirements where ignition sources are in close 3501 proximity to a barrier were not included based on discussions in IEC TC 108 and 3502 current practice for IEC 60950-1 enclosures. There is fire test data (barrier 3503 testing from IEC 60065) indicating that 2 mm thick (or greater) V-0 barriers and 3504 5 VA barriers have sufficient flame resistance to minimize a risk of creating 3505 openings when used in direct contact with PIS’s. Good HWI or HAI tests are not 3506 available internationally to address the distance from ignition sources to fire 3507 enclosure and barriers. The fire team has chosen to use the needle flame test 3508 as a surrogate test (similar to that done for barriers). 3509
6.5.1 General requirements 3510
Source: IEC 60332-1-2, IEC 60332-2-2 3511
– 106 – 108/757/DC Rationale: Wiring flammability proposals have now been included for all wiring (external 3512
and internal). 3513
Compliance with IEC 60332-1-2 for large wires and IEC 60332-2-2 for small 3514 wires has historically proven adequate for mains wiring. These documents 3515 include their own material flammability requirements. 3516
The requirements of IEC TS 60695-11-21 are also considered adequate given 3517 that the flame spread requirements for vertical testing are more onerous than 3518 the IEC 60332 series of documents. 3519
The compliance criteria are based on application of the above test methods. 3520 These are consistent with international wiring standards. National standards 3521 may have more onerous requirements. 3522
6.5.2 Requirements for interconnection to building wiring 3523
Source: IEC 60950-1:2005 3524
Rationale: Externally interconnected circuits that are intended for connection to 3525 unprotected building wiring equipment can receive sufficient power from the 3526 product to cause ignition and spread of fire with the building wall, ceiling, or 3527 remotely interconnected equipment. These requirements limit the power 3528 available to connectors/circuits intended for interconnection to specific types of 3529 wiring where the product is responsible for protection of that wiring. 3530
Where a circuit is intended for connection to equipment that is directly adjacent 3531 to the equipment, 6.6 prescribes the appropriate safeguards and limits 3532 associated for PS2 and PS3 sources. 3533
Telecommunication wiring is designed based on the expected power from the 3534 network. The requirements of IEC 60950-1 were considered adequate and were 3535 included. Wiring in this application should be equivalent to 0,4 mm diameter 3536 wiring (26 AWG) and have a default 1,3 A current limit established. This value 3537 has been used in IEC 60950-1 for the smaller telecommunication wiring. 3538
For some building wiring, the PS2 and PS3 safeguards are not considered 3539 adequate in some countries for connection to building wiring where that wiring 3540 is run outside of the conduit or other fire protective enclosures. The 3541 requirements for this clause come directly from requirements in IEC 60950-1, 3542 2.5 for circuits identified as limited power circuits. These requirements have 3543 proven to be historically adequate for connection of IT equipment to building 3544 wiring in these jurisdictions. 3545
The values used and protection requirements included in IEC 60950-1 and 3546 included in Annex Q.1 came from the building and fire codes requiring this 3547 protection. 3548
These requirements do not apply to connectors/circuits intended for 3549 interconnection of peripheral equipment used adjacent to the equipment. 3550
This requirement is also important for the use of ICT equipment in environments 3551 subject to electrical codes such as National Fire Protection Association NFPA 3552 70, which permit the routing of low power wiring outside of a fire containment 3553 device. 3554
Annex Q.1 was based on requirements from IEC 60950-1 that are designed to 3555 comply with the external circuit power source requirements necessary for 3556 compliance with the electrical codes noted above. 3557
6.6 Safeguards against fire due to the connection of additional equipment 3558
Source: IEC 60950-1 3559
Rationale: This subclause addresses potential fire hazards due to the connection of 3560 accessories or other additional equipment to unknown power source 3561 classifications. Most common low-voltage peripherals are not evaluated for 3562 connection to PS3 and therefore power sources should be identified. This is a 3563 current requirement of IEC 60950-1. 3564
– 107 – 108/757/DC Where the interconnected devices are known (device requirements are 3565
matched to the appropriate power source), this requirement for safeguard is not 3566 necessary. 3567
___________ 3568
7 Injury caused by hazardous substances 3569
Rationale: The majority of chemical injuries arise from inhalation or ingestion of chemical 3570 agents in the form of vapours, gases, dusts, fumes and mists, or by skin contact 3571 with these agents (see Table 15 in this document). The degree of risk of 3572 handling a given substance depends on the magnitude and duration of exposure. 3573 These injuries may be either acute or chronic. 3574
Many resins and polymers are relatively inert and non-toxic under normal 3575 conditions of use, but when heated or machined, they may decompose to 3576 produce toxic by-products. 3577
Toxicity is the capacity of a material to produce injury or harm when the chemical 3578 has reached a sufficient concentration at a certain site in the body. 3579
Potentially hazardous chemicals in the equipment are either: 3580
− as received in consumable material or items, such as printer cartridges, 3581 toners, paper, cleaning fluids, batteries; 3582
− produced under normal operating conditions as a by-product of the normal 3583 function of the device (for example, dust from paper handling systems, ozone 3584 from printing and photocopying operations, and condensate from air 3585 conditioning/de-humidifier systems); or 3586
− produced under abnormal operating conditions or as a result of a fault. 3587
It is essential to: 3588
− determine what substances are present in relative amounts in the equipment 3589 or could be generated under normal operating conditions; and 3590
− minimize the likelihood of injury to a person due to interaction with these 3591 substances. 3592
NOTE In addition to their potential toxicity, loss of containment of chemical materials may cause 3593 or contribute to failure of safeguards against fire, electric shock, or personal injury due to spillages. 3594
The number of different chemical materials that may be used in the wide variety 3595 of equipment covered by this document makes it impossible to identify specific 3596 hazards within the body of this document. Information needs to be sought by 3597 equipment manufacturers from the material suppliers on the hazards associated 3598 with their products and their compliance with any national and/or governmental 3599 regulations on the use and disposal of such materials. 3600
Energy source: 3601
The energy source for most chemically-caused injuries is ultimately the ability of 3602 a material to chemically react with human tissue, either directly or indirectly. The 3603 exception would be inert materials that can damage tissues by preventing them 3604 from functioning by limiting certain chemical reactions necessary for life. An 3605 example of this would be types of dust, which do not react with lung tissue, but 3606 prevent air from reaching the bloodstream. The reactions may be very energetic 3607 and damaging, such as acids on the skin, or can be very slow, such as the 3608 gradual build-up of substances in human tissues. 3609
Transfer mechanism: 3610
Transfer can only occur when chemical energy makes contact with human tissue. 3611 The routes for contact with human tissue are through the skin [or any outer 3612 membrane such as the eyes or nasal lining] (absorption), through the digestive 3613 tract (digestion), or through the lungs (inhalation). The route taken will depend 3614 largely on the physical form of the chemical: solid, liquid, or gas. 3615
– 108 – 108/757/DC
Injury: 3616
An injury can be either acute or chronic. Acute injuries are injuries with 3617 immediate and serious consequences (for example, a strong acid in the lungs) 3618 or the injury can be mild and result in irritation or headache. Chronic injuries are 3619 injuries with long term consequences and can be as serious as acute injuries 3620 (for example, consequences of long-term exposure to cleaning solvents). 3621
In most cases, the difference is the quantity and lethality of the toxic substance. 3622 A large amount of acetone can lead to death; a small amount may simply result 3623 in a headache. Many chemical compounds essential to life in small quantities 3624 (for example, zinc, potassium and nickel) can be lethal in larger amounts. The 3625 human body has different degrees of tolerance for different hazardous chemical 3626 substances. Exposure limits may be controlled by government bodies for many 3627 chemical substances. Where the use of hazardous chemical substances in 3628 equipment cannot be avoided, safeguards shall be provided to reduce the 3629 likelihood of exceeding the exposure limits. 3630
The different types of chemical hazards are identified in Table 15 and Figure 35 3631 in this document demonstrating the hierarchy of hazard management. 3632
Table 15 – Control of chemical hazards 3633
Transfer mechanism Prevention / safeguards
Ingestion, inhalation, skin contact, or other exposure to potentially hazardous chemicals
Hierarchy of hazard management:
1. Eliminate the chemical hazard by avoiding the use of the chemical.
2. Reduce the chemical hazard by substitution of a less hazardous chemical.
3. Minimize the exposure potential of the chemical by containment, ventilation and/or reduced quantities of the chemicals.
4. Use of personal protective equipment (PPE).
5. Provide use information and instructional safeguards.
Exposure to excessive concentrations of ozone during equipment operation
Hierarchy of hazard management:
1. Where possible, minimize the use of functions that produce ozone.
2. Provide adequate room ventilation.
3. Provide filtration to remove ozone.
Explosion caused by chemical reaction during use
Hierarchy of hazard management:
1. Eliminate the explosive charge.
2. Reduce the amount of explosive charge to the least amount possible.
3. Minimize hazard by the means of vents.
4. Provide use information and instructional safeguards.
3634
3635
– 109 – 108/757/DC
3636
Figure 35 – Flowchart demonstrating the hierarchy of hazard management 3637
3638
– 110 – 108/757/DC
Chemical hazards may also degrade or destroy the safeguards provided for 3639 other hazards such as fire and electric shock (for example, ozone attack on 3640 electrical insulation or corrosion of metallic parts). Chemical spillages or loss of 3641 containment can also lead to other hazards such as electric shock or fire 3642 depending on the location of any spillage and proximity to electric circuits. The 3643 same methods used for chemical health exposure control should also protect 3644 against such liquid spillages. 3645
Using a hazard-based engineering approach, Figure 36 in this document shows 3646 the main types of chemical health hazards and their transfer mechanisms. 3647
3648
Figure 36 – Model for chemical injury 3649
_____________ 3650
8 Mechanically-caused injury 3651
8.1 General 3652
Rationale: Mechanically caused injury such as cuts, bruises, broken bones, etc., may be 3653 due to relative motion between the body and accessible parts of the equipment, 3654 or due to parts ejected from the equipment colliding with a body part. 3655
8.2 Mechanical energy source classifications 3656
Purpose: To differentiate between mechanical energy source levels for normal operating 3657 conditions, abnormal operating conditions and single fault conditions 3658 applicable to each type of person. 3659
8.2.1 General classification 3660
Table 35 Classification for various categories of mechanical energy sources 3661
Line 3 – Moving fan blades 3662
Rationale: The acceptance criteria is based upon any number of factors such as location, 3663 but the key factor for judging acceptance is based upon the K factor, the 3664 relationship between mass (m) in kg, radius (r) in mm and speed (N) in rpm. This 3665 relationship can be used to find the K factor for the fan. Fans with a low K factor 3666 and low speeds are considered safer. See Figure 47 and Figure 48 for MS1 3667 values. An MS2 fan requires an instructional safeguard in addition to the 3668 limitation on the K factor value and the speed of the fan. The need for the 3669 relevant safeguard is based on the classification of fans. The K factor formula 3670 is taken from the UL standard for fans, UL 507 (which is based on a University 3671 of Waterloo study of fan motors). 3672
Single fault condition on a fan includes, but is not limited to, inappropriate input 3673 voltage due to the fault of a voltage regulator located upstream. 3674
As plastic fan blades are regarded less hazardous than metal fan blades, 3675 different values are used to determine separation between energy class 2 and 3676 class 3. 3677
– 111 – 108/757/DC
Typical parameters for fans used in products covered by this document are as 3678 follows: 3679
− fan mass (m) = about 25 g or 0,025 kg; 3680
− fan diameter (r) = 33 mm; 3681
− fan speed (N) = 6 000 rpm (maximum speed when the system is hottest, 3682 slower if the system is cool). 3683
Line 4 – Loosening, exploding or imploding parts 3684
Rationale: IEC TC 108 has tried to come up with specific requirements for solid rotating 3685 media. However, the result became too complex to be useful at this time. 3686
Line 5 – Equipment mass 3687
Rationale: The values chosen align with some commonly used values today. However, it is 3688 noticed that these are not completely reflecting reality and not a very good 3689 hazard-based approach. IEC TC 108 plans to work on these values in the future. 3690
Line 6 – Wall/ceiling or other structure mount 3691
Rationale: The values chosen align with some commonly used values today. However, it is 3692 noticed that these are not completely reflecting reality and not a very good 3693 hazard-based approach. IEC TC 108 plans to work on these values in the future. 3694
Notes b and c 3695
Rationale: The current values are based on experience and basic safety publications. 3696
8.2.2 MS1 3697
Rationale: Safe to touch. No safeguard necessary. 3698
8.2.3 MS2 3699
Rationale: Contact with this energy source may be painful, but no injury necessitating 3700 professional medical assistance occurs, for example, a small cut, abrasion or 3701 bruise that does not normally require professional medical attention. A 3702 safeguard is required to protect an ordinary person. 3703
8.2.4 MS3 3704
Rationale: An injury may occur that is harmful, requiring professional medical assistance. 3705 For example, a cut requiring stitches, a broken bone or permanent eye damage. 3706 A double or reinforced safeguard is required to protect an ordinary person 3707 and an instructed person. 3708
8.3 Safeguards against mechanical energy sources 3709
Purpose: To determine the number of safeguards needed between the type of person and 3710 the relevant energy source classification. 3711
Rationale: An instructional safeguard describing hazard avoidance may be employed to 3712 circumvent the equipment safeguard permitting access to MS2 part locations 3713 to perform an ordinary person service function. The instructional safeguard 3714 indicates that the equipment safeguard be restored after the service activity 3715 and before power is reconnected. When an instructional safeguard is allowed, 3716 a warning is also required to identify insidious hazards. 3717
For an instructed person and a skilled person, an instructional safeguard, 3718 in the form of a warning marking, is necessary to supplement the instruction they 3719 have received to remind them of the location of hazards that are not obvious. 3720
However, for a skilled person, an equipment safeguard is required in the 3721 service area of large equipment with more than one level 3 energy sources, 3722 where the skilled person can insert their entire head, arm, leg or complete body. 3723 This safeguard is intended to protect the skilled person against unintentional 3724 contact with any other level 3 energy source due to an involuntary startle reaction 3725 to an event in the equipment while servicing intended parts. 3726
– 112 – 108/757/DC The involuntary reaction may occur for a number of reasons, such as an 3727
unexpected loud noise, an arc flash or receipt of a shock, causing the person to 3728 recoil away from the energy source or part being serviced. Where more than one 3729 of the level 3 energy sources may require servicing at some time, removable 3730 equipment safeguards shall be designed such that any level 3 sources not 3731 being serviced can remain guarded. The equipment safeguards for this purpose 3732 only need to protect against larger body contact, since the potential involuntary 3733 recoil reaction will likely be full limb or body and not small body parts. 3734
8.4 Safeguards against parts with sharp edges and corners 3735
Rationale: Engineering judgment shall be used to class a mechanical energy source as 3736 MS1, MS2 or MS3 and an appropriate safeguard shall be provided. Where a 3737 MS2 or MS3 cannot be fully guarded without interfering with the intended 3738 function of the equipment, it shall be guarded as much as practical. Such an 3739 energy source shall not be accessible to children and be obvious to an adult. 3740 Instructional safeguards shall be provided to warn the person about potential 3741 contact with the energy source and what steps to take to avoid unintentional 3742 contact. 3743
We rely on engineering judgment as there are too many variables involved to 3744 define the type of edge or corner combined with the applied force and direction 3745 of contact or to provide specific values. 3746
8.5 Safeguards against moving parts 3747
Rationale: Enclosures and barriers protect against access to hazardous moving parts. See 3748 8.5.1 for the exception of requirements related to parts not fully guarded because 3749 of their function in the equipment. 3750
8.5.1 Requirements 3751
Rationale: The MS2 or MS3 energy sources need to be guarded against accidental access 3752 by a person's extremities, jewellery that may be worn, hair and clothing, etc. 3753 Access is determined by applying the appropriate tool from Annex V, and no 3754 further testing is necessary. We note that while it may be technically possible 3755 for some jewellery and hair to enter an opening smaller than the test finger, in 3756 such cases, the jewellery strands would have to be very thin and flexible enough 3757 to enter (as would a few strands of hair). As such while some pain may result if 3758 they happen to be caught in the mechanical device, it is deemed unlikely an 3759 injury would occur as described by this document. The residual risk can be 3760 considered a MS2 energy source at most. 3761
8.5.4.3 Equipment having an electromechanical device for destruction of media 3762
Source: UL/CSA 60950-1 second edition [national difference] 3763
Rationale: Recent large scale introduction of media shredders into the home environment 3764 resulted in an increase of children being injured when inserting their fingers 3765 through the shredder openings. These incidents were studied and a new probe 3766 was developed to assess potential access by children. The new probe/wedge 3767 has been designed for both application with force when inserted into the 3768 shredder openings and assessment of access to MS3 moving parts by a 3769 population consisting of both adults and children. This design differs from the 3770 existing UL and IEC accessibility probes since the UL Articulated Accessibility 3771 Probe is not intended to be used with a force applied to it, and the current IEC 3772 probes, while having an unjointed version for application under force, do not 3773 adequately represent the population for both adults and children. 3774
Because cross-cut shredders typically apply more force to the media than 3775 straight-cut shredders, the requirements include differentiated application forces 3776 for the two designs. The force values consider typical forces associated with 3777 straight-cut and cross-cut designs, taking into account data generated by the 3778 USA Consumer Product Safety Commission on typical pull forces associated 3779 with both strip type and crosscut type shredders. 3780
– 113 – 108/757/DC The dimensions of the new probe/wedge are based on the data generated during 3781
the development of the UL Articulated Accessibility Probe. However, the 3782 dimensions of the UL Articulated Accessibility Probe were defined in 3783 consideration of causal handling of products. Because of this, the 95th percentile 3784 points from the data were used to define the UL Articulated Accessibility Probe. 3785 The thickness and length dimensions of the new proposed probe/wedge have 3786 been developed in consideration of all data points. Articulation points are 3787 identical to those for the UL Articulated Accessibility Probe. 3788
8.6 Stability of equipment 3789
Source: IEC 60950-1 and IEC 60065 3790
Purpose: To align existing practice with the MS1, MS2 and MS3 energy. 3791
Rationale: Equipment weighing more than 25 kg is considered MS3. Regardless of weight, 3792 equipment mounted to the wall or ceiling is considered MS3 when it is to be 3793 mounted above 2 m height. 3794
Equipment weighing between 7 kg and not exceeding 25 kg is considered MS2. 3795 Equipment with a weight of 1 kg or more and that is mounted to the wall or ceiling 3796 to a maximum height of 2 m is also considered MS2. 3797
Equipment with weight not exceeding 7 kg is considered MS1 if floor standing, 3798 but can be either MS2 or MS3 if mounted to the wall or ceiling. Also see carts 3799 and stands, and wall or ceiling mounted equipment. 3800
Children are naturally attracted to moving images and may attempt to touch or 3801 hold the image by pulling or climbing up on to the equipment. The tests assess 3802 both the static stability and mounting grip when placed on a slippery surface 3803 such as glass. Children might also misuse controls that are readily available to 3804 them. 3805
8.6.2.2 Static stability test 3806
Rationale: Equipment is assessed for stability during expected use by applying force 3807 horizontally and downward on surfaces that could be used as a step or have 3808 other objects placed upon it. 3809
The value of 1,5 m was chosen as the maximum height where an average person 3810 could lean on or against the product. 3811
The 1,5 m is also used for table top equipment, since we do not know whether 3812 the product is going to be placed on a table or, if so, what the height of the table 3813 will be. 3814
8.6.2.3 Downwards force test 3815
Rationale: The height of 1 m represents the maximum height one could expect that people 3816 could try to use as a step to reach something. 3817
8.6.3 Relocation stability 3818
Source: IEC 60950-1 and IEC 60065 3819
Rationale: The 10° tilt test simulates potential horizontal forces applied to the equipment 3820 either accidentally or when attempting to move the equipment. In addition it 3821 simulates moving the equipment up a ramp during transport. 3822
The test on the horizontal support may be necessary (for example, for equipment 3823 provided with small feet, casters or the like). 3824
8.6.4 Glass slide test 3825
Source: IEC 60065:2011 3826
Purpose: To address the hazard of equipment with moving images sliding off a smooth 3827 surface when a child attempts to climb onto the equipment. 3828
– 114 – 108/757/DC Rationale: To ensure the display does not slide too easily along a smooth surface that could 3829
result in the display falling from an elevated height on to a child. 3830
8.6.5 Horizontal force test and compliance criteria 3831
Purpose: To simulate the force of a child climbing up on to equipment with front mounted 3832 user controls or with moving images. 3833
Rationale: Field data and studies in the US have shown that children 2-5 years of age were 3834 attracted to the images on the display that may result in the child climbing onto 3835 the display to touch/get close to the image. The equipment could then tip over 3836 and crush the child. Also, products with accessible controls or that are shorter 3837 than 1 m in height are considered likely to be handled by children. 3838
− Data was gathered in the 1986 to 1998 for CRT TV sets ranging from 48,26 cm 3839 to 68,58 cm (19 to 27 inches). The average horizontal force was 13 % of the 3840 equipment weight. 3841
− The 15° tilt test (an additional 5° over static stability test) provides an 3842 additional safety factor. 3843
8.7 Equipment mounted to a wall, ceiling or other structure 3844
Source: IEC 60065 and 60950 series 3845
Purpose: The objective of this subclause is to minimize the likelihood of injury caused by 3846 equipment falling due to failure of the mounting means. 3847
Rationale: Equipment intended to be mounted to a wall or ceiling should be tested to ensure 3848 adequacy for all possible mounting options and all possible failure modes. For 3849 typical equipment, such as flat panel televisions, mounting bosses are usually 3850 integrated into the equipment and used with an appropriate wall or ceiling 3851 mounting bracket to attach to a wall or ceiling. Typical mounting bosses are 3852 comprised of threaded inserts into the rear panel of the equipment. 3853
The appropriate load is divided by the number of mounting means (for example, 3854 mounting bosses) to determine the force applied to each individual mounting 3855 means. 3856
The horizontal force values of 50 N and 60 s have been successfully used for 3857 products in the scope of these documents for many years. 3858
8.7.2 Test methods 3859
Figure 37 in this document gives a graphical view of the different tests required by 3860 Test 2 and show the directions that the forces are applied. 3861
3862
Figure 37 – Direction of forces to be applied 3863
– 115 – 108/757/DC Table 37 Torque to be applied to screws 3864
Source: IEC 60065 3865
Rationale: These torque values have been successfully used for products in the scope of 3866 this document for many years. 3867
8.8 Handle strength 3868
Source: IEC 60065 and IEC 60950-1 3869
Rationale: A handle is a part of the equipment that is specifically designed to carry the 3870 equipment or subassembly around. A grip which is made for easy removal or 3871 placement of a subassembly in an equipment is not considered to be a handle. 3872
The 75 mm width simulates the hand width. The safety factors take into account 3873 the acceleration forces and additional stresses that could be applied due to extra 3874 weight on top of the equipment when being lifted. The safety factor is less at the 3875 higher weight (MS3) because the equipment would be lifted more slowly, 3876 reducing the acceleration force, and there is less probability that extra weight 3877 would be added before lifting, as this would exceed the normal weight to be lifted 3878 by one person without assistance of a tool. Equipment classed as MS1 with 3879 more than one handle could be used to support additional objects when being 3880 carried and should be tested. 3881
8.8.2 Test method 3882
Rationale: There is no test for MS1 with only one handle. Having 2 handles facilitates 3883 transporting the equipment while carrying additional objects adding stress to the 3884 handles. 3885
8.9 Wheels or casters attachment requirements 3886
Purpose: To verify that wheels or casters are securely fixed to the equipment. 3887
Source: UL 1667 3888
Purpose: For wheel size, reduce the likelihood of the equipment on the cart or stand 3889 tipping while being moved from room to room where the wheels may encounter 3890 a variety of obstacles, such as: friction of different surfaces (for example, 3891 transition from a hard surface over carpet edging), cables, and doorway sills. 3892
Rationale: The 100 mm min wheel size was found to be adequate to enable rolling over 3893 these obstacles without abruptly stopping that could cause the cart or stand to 3894 tip, or the equipment located on the cart or stand to slide off. 3895
8.10 Carts, stands, and similar carriers 3896
Source: UL 60065 3897
Rationale: To avoid tipping, the 20 N test simulates cart wheels being unintentionally 3898 blocked during movement. 3899
8.10.1 General 3900
Source: IEC 60065 3901
Rationale: A wheel of at least 100 mm diameter can be expected to climb over usual 3902 obstacles such as electrical cords, door jambs, etc., and not be halted suddenly. 3903
8.10.2 Marking and instructions 3904
Rationale: Various means of marking may apply depending on the method of associating 3905 the equipment with a particular cart, stand of similar carrier. 3906
– 116 – 108/757/DC 8.10.3 Cart, stand or carrier loading test and compliance criteria 3907
Source: IEC 60065 3908
Purpose: To verify that a cart or stand can withstand foreseeable overloading without 3909 creating a hazardous situation. 3910
Rationale: The 220 N force simulates the weight of a small child approximately 5 years of 3911 age, who may attempt to climb onto the cart or stand. The 30 mm circular 3912 cylinder simulates a child’s foot. The 750 mm height is the approximate access 3913 height of the 5-year-old child. The additional 440 N force test simulates potential 3914 additional materials or equipment being placed on the cart or stand. The 3915 additional 100 N simulates overloading by the user. Testing has been limited to 3916 1 min as experience has shown that the likelihood of a test failure will occur 3917 within that time. 3918
8.10.4 Cart, stand or carrier impact test 3919
Purpose: To verify that a cart or stand can withstand a foreseeable impact without creating 3920 a hazardous situation. 3921
Source: IEC 60065 and IEC 60950 series 3922
Rationale: The 7 joules simulate intentional and accidental contact with the equipment and 3923 come from the T.6 enclosure test. 3924
8.10.5 Mechanical stability 3925
Purpose: To verify that a cart or stand remains stable under specified loading. The 3926 equipment installed on the cart may come loose, but not fall off the cart. 3927
Rationale: The weight of the force test is reduced to 13 % should the equipment on the cart 3928 or stand move, as the equipment would then be considered separately from the 3929 cart or stand. When the equipment does not move during the force test, together 3930 they are considered a single unit. 3931
8.10.6 Thermoplastic temperature stability 3932
Source: IEC 60065 and IEC 60950-1 3933
Rationale: Intended to prevent shrinkage, relaxation or warping of materials that could 3934 expose a hazard. 3935
8.11 Mounting means for slide-rail mounted equipment (SRME) 3936
8.11.1 General 3937
Source: UL/CSA 60950-1 second edition 3938
Rationale: The potential hazardous energy source is a product that contains significant 3939 mass, and which is mounted on slide-rails in a rack. A joint US/Canadian Adhoc 3940 researched and developed these requirements based on hazard-based 3941 assessment and tests. 3942
The center of gravity was chosen to apply the downward force because in 3943 general, when installing equipment in a rack, it is foreseeable that previously 3944 installed equipment of similar size/mass may be pulled out into the service 3945 position (fully extended) and used to set the new equipment on while positioning 3946 and installing the new slide/rails. In this scenario, it is not likely that the new 3947 equipment would be significantly off-centre from the installed equipment that it 3948 is being set on. 3949
Vertically mounted SRMEs are not addressed in this document. 3950
– 117 – 108/757/DC 8.11.3 Mechanical strength test 3951
Purpose: To simulate temporary placement of another server on top of an existing one 3952 during installation of the new one. So the test is the downward force. 3953
Rationale: 50 % of the equipment mass is derived from the mass of the equipment, and a 3954 50 % tolerance allowed for manufacturing differences in the rails which 3955 effectively adds a safety buffer. 3956
The 330 N to 530 N additional force accounts for equipment that is about to be 3957 installed in a rack being placed or set on a previously installed piece of 3958 equipment where the previously installed equipment is being used as a 3959 temporary shelf or work space. It is estimated that 530 N is the maximum mass 3960 of equipment allowed to be safely lifted by two persons without the use of 3961 mechanical lifting devices. Equipment having a mass greater than 530 N will 3962 have mechanical lifting devices and it is therefore unlikely that the equipment 3963 being installed will be set on any equipment previously installed in the rack. 3964
Taking the actual installation environment into consideration, an additional force 3965 is limited to maximum 800 N (average weight of an adult man) that is same value 3966 as the downward test force in 8.6.2.3. The 800 N value comes from 3967 IEC 60950-1:2005, 4.1 Stability. 3968
8.11.3.2 Lateral push foce test 3969
8.11.3.3 Integrity of slide rail end stops 3970
Source: UL/CSA 60950-1 second edition 3971
Purpose: To simulate maintenance on the server itself, by smaller applying forces 3972 equivalent to what is expected during subassembly and card replacement, etc. 3973 So this also tests the laterally stability of the slide rails. It is not necessary to 3974 retest the downward vertical force if it is already tested for 8.11.3, but that should 3975 be common sense when preparing a test plan. 3976
The cycling of the slide rail after the tests ensures they have not been bent in a 3977 way that could easily fly apart after the service operation. 3978
Rationale: The 250 N force is considered a force likely to be encountered during servicing 3979 of the equipment, and normal operations around equipment. The force is partially 3980 derived from the existing IEC 60950-1:2005, 4.1, and partially from research into 3981 normally encountered module plug forces seen on various manufacturers’ 3982 equipment. The application of force at the most unfavourable position takes into 3983 account the servicing of a fully extended piece of equipment, leaning on or 3984 bumping into an extended piece of equipment and other reasonably foreseen 3985 circumstances which may be encountered. 3986
___________ 3987
9 Thermal burn injury 3988
9.1 General 3989
Source: ISO 13732-1:2006 and IEC Guide 117 3990
Rationale: A General 3991
A burn injury can occur when thermal energy is conducted to a body part to 3992 cause damage to the epidermis. Depending on the thermal mass of the object, 3993 duration of contact and exposure temperature, the body response can range 3994 from perception of warmth to a burn. 3995
The energy transfer mechanism for equipment typically covered by the document 3996 is via conduction of thermal energy through physical contact with a body part. 3997
The likelihood of thermal injury is a function of several thermal energy 3998 parameters including: 3999
− temperature difference between the part and the body; 4000
– 118 – 108/757/DC
− the thermal conductivity (or thermal resistance) between the hot part and the 4001 body; 4002
− the mass of the hot part; 4003
− the specific heat of the part material; 4004
− the area of contact; 4005
− the duration of contact. 4006
B Model for a burn injury 4007
A skin burn injury occurs when thermal energy impinges on the skin and raises its 4008 temperature to a level that causes cell damage. The occurrence of a burn will 4009 depend on several parameters. The hazard based three block model applied to the 4010 occurrence of a burn (see Figure 38 in this document) takes account of not just the 4011 temperature of the source, but its total thermal energy, which will depend on its 4012 temperature (relative to the skin), as well as its overall heat capacity. The model 4013 also takes account of the energy transfer mechanism, which will depend on the 4014 thermal conductivity between the body and the thermal source as well as the area 4015 and duration of contact. The occurrence and severity of a burn will depend on the 4016 amount of thermal energy transferred. 4017
4018
Figure 38 – Model for a burn injury 4019
Normally, the energy transfer mechanism from the energy source to a body part 4020 is through direct contact with the body part and sufficient contact duration to 4021 allow transfer of thermal energy causing a burn. The higher the temperature of 4022 the thermal source and the more efficient the transfer mechanism, the shorter 4023 the contact time becomes before the occurrence of a burn. This is not a linear 4024 function and it is dependent on the material, the temperature and the efficiency 4025 of the thermal transfer. The following examples demonstrate the impact of this 4026 non-linear relationship to short-term/high temperature and longer term/lower 4027 temperature contact burns. 4028
Example 1: An accessible metal heat sink at a temperature of 60 °C may have 4029 sufficient energy to cause a burn after contact duration of about 5 s. At a 4030 temperature of 65 °C, a burn may occur after contact duration of just 1,5 s (see 4031 IEC Guide 117:2017, Figure A.1). As the temperature of the metal surface 4032 increases, the contact time necessary to cause a burn decreases rapidly. 4033
Example 2: Consider a thermal source with low to moderate conductivity such 4034 as a plastic enclosure. At a temperature of 48 °C, it may take up to 10 min for 4035 the transfer of sufficient thermal energy to cause a burn. At 60 °C, a burn may 4036 occur after contact duration of just 1 min (see IEC Guide 117:2010, Table A.1). 4037 Although the temperature of the source has increased by just 25 %, the contact 4038 time necessary to cause a burn threshold has decreased by 90 %. 4039
In practice, the actual thermal energy and duration of exposure required to cause 4040 a burn will also depend on the area of contact and condition of the skin. For 4041 simplification of the model and based upon practice in the past, it is assumed 4042 that the contact area will be ≤ 10 % of the body and applied to healthy, adult 4043 skin. 4044
– 119 – 108/757/DC As a general rule, low temperature devices are likely to cause a heating or pain 4045
sensation before causing a significant burn to which ordinary persons will 4046 normally respond (see ISO 13732-1:2009, Note of 5.7.3). Requirements for 4047 persons with impaired neurological systems are not considered in this document 4048 but may be considered in the future. 4049
NOTE 1 The impact of surface area contact is not being addressed in this paper at this time and 4050 is an opportunity for future work. Use and coverage of large contact areas as might occur in medical 4051 applications of heating pads covering more than 10 % of the body surface are outside the scope 4052 of this document, as this type of application is more appropriate to medical device publications. 4053
NOTE 2 The pressure of the contact between the thermal source and the body part can have an 4054 impact on the transfer of thermal energy. Studies have shown this effect to have appreciable impact 4055 at higher pressures. For typical pressures associated with casual contact up to a pressure of 20 N 4056 the effect has been shown to be negligible, and thus contact pressure is not considered in this 4057 document (Ref: ATSM C 1055, X1.2.3.4, ASTM C 1057,7, Note 10). 4058
NOTE 3 Considerations for burns generated by infrared (IR), visible, ultra violet light radiation 4059 and RF radiation sources are outside the scope of Clause 9 dealing with thermal burn injury. 4060
C Types of burn injuries 4061
Burn injuries are commonly classed as first degree, second degree or third 4062 degree in order of increasing severity: 4063
First degree burn: the reaction to an exposure where the intensity or duration 4064 is insufficient to cause complete necrosis of the epidermis. The normal response 4065 to this level of exposure is dilation of the superficial blood vessels (reddening of 4066 the skin). No blistering occurs. (Reference: ASTM C1057) 4067
Second degree burn: the reaction to an exposure where the intensity and 4068 duration is sufficient to cause complete necrosis of the epidermis but no 4069 significant damage to the dermis. The normal response to this exposure is 4070 blistering of the epidermis. (Reference: ASTM C1057) 4071
Third degree burn: the reaction to an exposure where significant dermal 4072 necrosis occurs. Significant dermal necrosis with 75 % destruction of the dermis 4073 is a result of the burn. The normal response to this exposure is open sores that 4074 leave permanent scar tissue upon healing. (Reference: ASTM C1057) 4075
ISO 13732-1, 3.5 classifies burns as follows: 4076
Superficial partial thickness burn – In all but the most superficial burns, the 4077 epidermis is completely destroyed but the hair follicles and sebaceous glands as 4078 well as the sweat glands are spared. 4079
Deep partial thickness burn: a substantial part of the dermis and all sebaceous 4080 glands are destroyed and only the deeper parts of the hair follicles or the sweat 4081 glands survive. 4082
Whole thickness burn: when the full thickness of the skin has been destroyed 4083 and there are no surviving epithelial elements. 4084
Although there is some overlap between the classifications in ASTM C1057 and 4085 those in IEC Guide 117, the individual classifications do not correspond exactly 4086 with each other. Further, it should be noted that the classifications of burns 4087 described here is not intended to correspond with the individual thermal source 4088 classifications (TS1, TS2, and TS3) described later in this document. 4089
D Model for safeguards against thermal burn injury 4090
To prevent thermally-caused injury, a safeguard is interposed between the body 4091 part and the energy source. More than one safeguard may be used to meet the 4092 requirements for thermal burn hazard protection. 4093
– 120 – 108/757/DC
Figure 39 – Model for safeguards against thermal burn injury
To prevent thermally-caused injury, a safeguard is interposed between the body 4094 part and the energy source (see Figure 39 in this document). More than one 4095 safeguard may be used to meet the requirements for thermal burn hazard 4096 protection. 4097
Safeguards overview 4098
This section shows examples of the different types of safeguards that may be 4099 applied: 4100
a) Thermal hazard not present 4101
The first model, see Figure 40 in this document, presumes contact to a surface 4102 by an ordinary person where a thermal hazard is not present. In this case, no 4103 safeguard is required. 4104
4105
Figure 40 – Model for absence of a thermal hazard 4106
b) Thermal hazard is present with a physical safeguard in place 4107
The second model, see Figure 41 in this document, presumes some contact with 4108 a surface by an ordinary person. The thermal energy source is above the 4109 threshold limit value for burns (Table 38), but there are safeguards interposed 4110 to reduce the rate of thermal energy transferred such that the surface 4111 temperature will not exceed the threshold limit values for the expected contact 4112 durations. Thermal insulation is an example of a physical safeguard. 4113
4114
Figure 41 – Model for presence of a thermal hazard 4115 with a physical safeguard in place 4116
c) Thermal hazard is present with a behavioural safeguard in place 4117
The third model, see Figure 42 in this document, presumes the possibility of 4118 some contact to the thermal source or part by an ordinary person. The 4119 temperature is above the threshold limit value but the exposure time is limited 4120 by the expected usage conditions or through instructions to the user to avoid or 4121 limit contact to a safe exposure time. The contact time and exposure will not 4122 exceed the threshold limit value. An additional safeguard may not be required. 4123
– 121 – 108/757/DC
4124
Figure 42 – Model for presence of a thermal hazard 4125 with behavioural safeguard in place 4126
9.2 Thermal energy source classifications 4127
Rationale: Surfaces that may be touched are classified as thermal energy sources TS1, 4128 TS2 or TS3 with TS1 representing the lowest energy level and TS3 the highest. 4129 The classification of each surface will determine the type of safeguards 4130 required. 4131
The assessment of thermal burn hazards is complex and, as discussed in the 4132 model for a burn injury above, involves several factors. Important aspects 4133 include the overall heat capacity of the source, its temperature relative to the 4134 body, thermal conductivity of the contact and others. To present a simple model 4135 for assessment of a given surface, it is assumed that the overall heat capacity 4136 and the thermal conductivity will remain constant. 4137
Thus, thermal energy sources are classified in terms of the material of the 4138 surface, its relative temperature and duration of contact only. Usually, for a given 4139 material the temperature and duration of contact are likely to be the only 4140 significant variables when assessing the risk of a burn injury. 4141
9.2.1 TS1 4142
Rationale: The lowest thermal energy source is TS1. TS1 represents a level of thermal 4143 energy that generally will not cause a burn injury. 4144
9.2.2 TS2 4145
Rationale: A TS2 thermal energy source has sufficient energy to cause a burn injury in 4146 some circumstances. The occurrence of a burn from a TS2 source will largely 4147 depend on the duration of contact. Depending on the contact time, and contact 4148 area, contact material, and other factors, a TS2 source is not likely to cause an 4149 injury requiring professional medical attention. Table 38 defines the upper limits 4150 for TS2 surfaces. 4151
A TS2 circuit is an example of a class 2 energy source where the basic 4152 safeguard may, in some cases, be replaced by an instructional safeguard. 4153 Details are given in Table 38, footnote e. 4154
9.2.3 TS3 4155
Rationale: A TS3 thermal energy source has sufficient energy to cause a burn injury 4156 immediately on contact with the surface. There is no table defining the limits for 4157 a TS3 surface because any surface that is in excess of TS2 limits is considered 4158 to be TS3. Within the specified contact time, as well as contact area, contact 4159 material and other factors, a TS3 source may cause an injury requiring 4160 professional medical attention. As TS3 surfaces require that maximum level of 4161 safeguard defined in the document. All surfaces may be treated as TS3 if not 4162 otherwise classified. 4163
– 122 – 108/757/DC Source: IEC Guide 117. 4164
Rationale: When doing the temperature measurements, an ambient temperature is used as 4165 described in 9.2.5 to measure the temperatures without taking into account the 4166 maximum ambient specified by the manufacturer. 4167
9.3 Touch temperature limits 4168
Table 38 Touch temperature limits for accessible parts 4169
Source: The limits in Table 38 are primarily derived from data in IEC Guide 117. 4170
Rationale: The temperature of the skin and the duration of raised temperature are the 4171 primary parameters in the occurrence of a skin burn injury. In practice, it is 4172 difficult to measure the temperature of the skin accurately while it is in contact 4173 with a hot surface. Thus the limits in Table 38 do not represent skin 4174 temperatures. These limits do represent the surface temperatures that are 4175 known to cause a skin burn injury when contacted for greater than the specified 4176 time limit. 4177
The thermal energy source criterion takes account of the temperature of the 4178 source, its thermal capacity and conductivity as well as the likely duration and 4179 area of contact. As the thermal capacity and conductivity will normally remain 4180 constant for a given surface, the limits here are expressed in degrees C for 4181 typical material types and contact durations. 4182
Contact time duration > 8 h 4183
For devices worn on the body (in direct contact with the skin) in normal use (> 4184 8 h), examples include portable, lightweight devices such watches, headsets, 4185 music players and sports monitoring equipment. Since the values in the table do 4186 not represent skin temperature as indicated above, measurements should not be 4187 done while wearing the devices. 4188
The value of 43 °C for all materials for a contact period of 8 h and longer assumes 4189 that only a minor part of the body (less than 10 % of the entire skin surface of 4190 the body) or a minor part of the head (less than 10 % of the skin surface of the 4191 head) touches the hot surface. If the touching area is not local or if the hot 4192 surface is touched by vital areas of the face (for example, the airways), severe 4193 injuries may occur even if the surface temperature does not exceed 43 °C (see 4194 IEC Guide 117). 4195
NOTE Prolonged exposure to 43 °C may result in erythema (temporary redness of the skin 4196 causing dilation of the blood capillaries) which will typically go away within a few hours after 4197 removal of the heat source. For some users, this may be misperceived as a burn. 4198
Contact time durations > 1 min 4199
For very long-term contact (> 10 min), the temperature below which a burn will 4200 not occur converges towards 43 °C for most materials (see IEC Guide 117:2010, 4201 Figure A.1). Studies carried out on portable IT Equipment have shown that for 4202 long term contact, a surface temperature will drop by between 5 °C and 12 °C 4203 when in contact with the body due to the cooling effect of the blood circulation. 4204 On this basis, and taking account of the probability that long-term contact will 4205 normally be insulated by clothing or some other form of insulation, the TS1 4206 temperature limit for contact periods greater than 1 min in Table 39 are 4207 conservatively chosen as 48 °C for all materials. 4208
Examples of products with surfaces where expected continuous contact 4209 durations greater than 1 min include joysticks, mice, mobile telephones, and 4210 PDAs. Any handles, knobs or grips on the equipment that are likely, under normal 4211 usage, to be touched or held for greater than 1 min are also included. 4212
– 123 – 108/757/DC Contact time durations between 10 s and 1 min 4213
For surfaces that are touched for shorter contact durations (up to 1 min), the 4214 temperature below which a burn will not occur is influenced by the material type 4215 as well as other factors. Because the contact time is shorter, there is insufficient 4216 time for heat transfer to cause the cooling effect described above, so it is not 4217 considered in the limits. The TS1 temperature limits in Table 38 for contact 4218 durations up to 1 min are taken directly from IEC Guide 117:2010, Table A.1. 4219
Examples of surfaces with contact durations up to 1 min include handles or grips 4220 used primarily for moving or adjusting the equipment. Also tuning dials or other 4221 controls where contact for up to 1 min may be expected. 4222
Contact time durations up to 10 s 4223
Even shorter-term contact may occur for surfaces such as push button/switch, 4224 volume control; computer or telephone keys. In this case, the surfaces will not 4225 normally be touched for a duration greater than 10 s. The TS1 temperature limits 4226 in Table 38 for these surfaces are based on the burn threshold limits in IEC 4227 Guide 117 for contact durations of up to 10 s. 4228
For surfaces that are accessible but need not be touched to operate the 4229 equipment, contact duration of up to 1 s is assumed. For healthy adults, a 4230 minimum reaction time of 0,5 s can be assumed. For more general applications, 4231 the reaction time increases to 1 s IEC Guide 117, Table 2. The TS1 temperature 4232 limits in Table 38 for these surfaces are based on the burn threshold limits in 4233 Guide 117 for contact durations of 1 s (see IEC Guide 117:2010, Figures A.1 – 4234 A.6). More conservative values than those in IEC Guide 117 are chosen for metal 4235 and glass to provide some margin against a reduced reaction time while in 4236 contact with a high thermal energy surface of high thermal conductivity. 4237
Examples of such parts include general enclosure surfaces, accessible print 4238 heads of dot matrix printers or any internal surfaces that may be accessible 4239 during routine maintenance. Accidental contact, with no intention to hold or 4240 contact the surface is also included. 4241
For contact durations between 1 s and 10 s, IEC Guide 117 provides temperature 4242 ranges over which a burn may occur rather than precise limits. This takes 4243 account of the uncertainty that applies to the occurrence of burn injury over 4244 shorter periods. The texture of the surface can also be a factor in the occurrence 4245 of a burn and this is not taken into account in the limits in IEC Guide 117. As 4246 most surfaces in IT equipment will have some texturing, values at the higher end 4247 of the spreads have been chosen. 4248
Contact time durations up to 1 s 4249
For accessible surfaces that are not normally intended or expected to be 4250 touched while operating or disconnecting the equipment, a contact time duration 4251 of up to 1 second is appropriate. This would apply to any surface of the 4252 equipment that does not have functionality when touched or is unlikely to be 4253 inadvertently contacted when accessing functional surfaces such as keyboards 4254 or handles. Typical and readily expected usage should be considered when 4255 assessing likely contact duration with such a surface. 4256
For example, it is not necessary to touch a direct plug-in external power supply 4257 adapter (Figure 43) during normal use of the equipment, but it will likely be 4258 touched or briefly held for disconnection from the mains. Thus, this type of 4259 equipment is expected to be contacted for more than one second. 4260
4261
– 124 – 108/757/DC
Figure 43 – Direct plug in Figure 44 – External power supply
4262
Other external power supplies, such as those often supplied with notebook 4263 computers and other equipment (Figure 44), with a connected power cord will 4264 not normally be touched either during usage or for disconnection. For external 4265 power supplies with power cord, to disconnect from mains, the user will grip the 4266 power cord plug. The contact time with the plug would be more than 1 second 4267 and the contact time of the power supply would be less than 1 second. 4268
Other considerations 4269
In the event of a fault condition arising, the user is less likely to touch the 4270 equipment and any contact with accessible surfaces is likely to be very brief. 4271 Thus higher limits than those allowed under IEC Guide 117 are permitted. For 4272 metal, glass and plastic surfaces, the limit is 100 °C (IEC 60065:2010, Table 3). 4273 For wood, a temperature of 150 °C was chosen because 100 °C would be lower 4274 than the normal temperature of 140 °C. 4275
When contact with a TS1 surface is unlikely due to its limited size or accessibility, 4276 a temperature up to 100 °C is acceptable if an instructional safeguard is 4277 provided on the equipment (see IEC 60950-1:2005, Table 4C, IEC 60065:2001, 4278 Table 3). 4279
In the case where a surface is hot in order to carry out its function, the occurrence 4280 of contact with the surface or a subsequent burn injury is unlikely if the user is 4281 made aware that the surface is hot. Thus, a temperature up to 100 °C or higher 4282 is acceptable if there is an effective instructional safeguard on the body of the 4283 equipment indicating that the surface is hot (see IEC 60950-1:2005, Table 4C 4284 and IEC 60065:2001, Table 3). 4285
Factors for consideration in determining test conditions 4286
For consistency with other parts of the document and to reflect typical user 4287 conditions, the ambient conditions described in B.1.6 apply. 4288
Assessment of safeguards should be carried out under normal operating 4289 conditions of the product that will result in elevated surface temperatures. The 4290 chosen normal operating conditions should be typical of the manufacturer’s 4291 intended use of the product while precluding deliberate misuse or unauthorized 4292 modifications to the product or its operating parameters by the user. For some 4293 simple equipment, this will be straightforward. For more complex equipment, 4294 there may be several variables to be considered including the typical usage 4295 model. The manufacturer of the equipment should perform an assessment to 4296 determine the appropriate configuration. 4297
Example: Factors that may be considered in determining the test conditions for 4298 a notebook computer: 4299
− Mode of operation 4300
• Variable CPU speed 4301
• LCD brightness 4302
− Accessories installed: 4303
• Number of disk drives 4304
• USB devices 4305
• External HDD 4306
− Software installed: 4307
• Gaming applications 4308
• Duration of continuous use 4309
• Long term contact likely? 4310
– 125 – 108/757/DC
• Other specialist applications 4311
− Battery status: 4312
• Fully charged/ Discharged 4313
• AC connected 4314
9.3.1 Touch temperature limit requirements 4315
Rationale: Table 38 provides touch temperature limits for accessible parts, assuming 4316 steady state. IEC Guide 117 provides the methodology to assess products with 4317 changing temperatures or small parts which are likely to drop in temperature 4318 upon touch. Using a thermesthesiometer for a specified time interval, the 4319 thermesthesiometer simulates the skin temperature of human finger and heating 4320 effects caused by contact with the product surface under test. Once contact is 4321 made, the thermesthesiometer and product under test will eventually reach 4322 thermal equilibrium at which point finger skin temperature can be determined. 4323
Background: The touch limits from Table 38 for > 1 s and < 10 s may be used for small hand-4324 held equipment with localized hotspots, given a small thermal energy source 4325 and touching can be easily avoided by changing holding position of the device. 4326
This same rationale would also apply to small multi-media peripherals which are 4327 removed from a host device (for example, USB memory stick, PCMCIA cards, 4328 SD card, Compact Flash card, ejectable media, etc.). In many cases, these 4329 peripherals may be removed from their host (for example, power source) 4330 exposing higher thermally conductive materials (for example, metals), but are in 4331 thermal decay (i.e. no longer powered). 4332
In cases of doubt, the method in IEC Guide 117 may be used for steady-state 4333 conditions. An example of a simplified method for thermally decaying parts is 4334 provided as a reference: 4335
Touch temperature limits in IEC Guide 117 are based on time-weighted exposure 4336 for burn (for example, thermal energy). As long as integrated thermal energy 4337 calculations (for example, area of temp vs. time) of the part at specified time 4338 intervals is less than the associated integrated thermal energy calculated limits 4339 over that duration, the measured temperatures should be acceptable. 4340
The most significant time internals to consider for decaying thermal energy is 4341 between 1 s to 10 min (using 10 s, 1 min, 10 min intervals). 4342
− For exposure times < 1 s, the 1 s temperature limits of the IEC Guide 117 4343 should be used for 2 reasons: 1) Reaction times – under general applications 4344 reaction times of < 1 s are not probable and greatest risk of burn. 2) 4345 Repeatability – temperature measurement capability < 1 s intervals is less 4346 common and more difficult to accurately calculate the part energy. 4347
− For exposure times > 10 min, the temperature limits of IEC Guide 117 should 4348 be used: after 10 min parts should either have cooled or reach sufficient 4349 equilibrium to utilize the temperature limits without the need for assessing 4350 thermal energy. 4351
This simplified method requires the part under test to be mounted using 4352 thermally insulating clamp. Clamp to the part’s least thermally conductive 4353 material and smallest contact needed to hold the part. Measured in still-air room 4354 ambient. 4355
NOTE Parts that are hand-held will decay faster than open-air measurements (for example, 4356 radiation and convection) owing to direct conduction of heat to skin. 4357
9.3.2 Test method and compliance criteria 4358
Rationale: The general intent of the requirements are to use an ambient temperature as 4359 follows without taking into account the maximum ambient specified by the 4360 manufacturer: 4361
− The test may be performed between 20 °C and 30 °C. 4362
– 126 – 108/757/DC
− If the test is performed below 25 °C, the results are normalized to 4363 25 °C. 4364
− If the test is performed above 25 °C, the results are not normalized to 25 °C 4365 and the limits (Table 38) are not adjusted. In case the product fails the 4366 requirements, the test may be repeated at 25 °C. 4367
9.4 Safeguards against thermal energy sources 4368
Rationale: TS1 represents non-hazardous energy and thus, no safeguard is required. 4369 Because the energy is non-hazardous, and there is no possibility of an injury, it 4370 may be accessible by ordinary persons and there is no restriction on duration 4371 of contact under normal operating conditions. 4372
TS2 represents hazardous energy that could cause a burn injury if the contact 4373 duration is sufficient. Therefore, a safeguard is required to protect an ordinary 4374 person. A TS2 surface will not cause a burn immediately on contact. Because 4375 the burn injury from a TS2 surface is likely to be minor and pain or discomfort is 4376 likely to precede the occurrence of a burn injury, a physical safeguard may not 4377 be required if there is an effective means to inform the ordinary person about 4378 the risks of touching the hot surface. 4379
Thus, a TS2 safeguard may be one of the following: 4380
− a physical barrier to prevent access; or 4381
− an instructional safeguard to limit contact time below the threshold limit 4382 value versus time. 4383
TS3 represents hazardous energy that is likely to cause a burn injury 4384 immediately on contact. Because a TS3 surface is always likely to cause a burn 4385 immediately or before the expected reaction time due to pain or discomfort, an 4386 equipment safeguard is required. 4387
Unless otherwise specified in the document, ordinary persons need to be 4388 protected against all TS2 and TS3 energy sources. 4389
Instructed persons are protected by the supervision of a skilled person and 4390 can effectively employ instructional safeguards. Thus, equipment 4391 safeguards are not required for TS2 energy sources. An instructional 4392 safeguard may be required. 4393
TS3 energy sources can cause severe burns after very short contact duration. 4394 Thus, an instructional safeguard alone is not sufficient to protect an instructed 4395 person and an equipment safeguard is required. 4396
Skilled persons are protected by their education and experience and are 4397 capable of avoiding injury from TS3 sources. Thus, an equipment safeguard is 4398 not required to protect against TS3 energy sources. As a pain response may 4399 cause an unintentional reflex action even in skilled persons, an equipment or 4400 instructional safeguard may be required to protect against other class 3 energy 4401 sources adjacent to the TS3 energy source. 4402
9.5.1 Equipment safeguard 4403
Rationale: The function of the equipment safeguard is to limit the transfer of hazardous 4404 thermal energy. An equipment safeguard may be thermal insulation or other 4405 physical barrier. 4406
9.5.2 Instructional safeguard 4407
Rationale: An instructional safeguard will inform any person of the presence of hazardous 4408 thermal energy. Instructional safeguards may be in a text or graphical format 4409 and may be placed on the product or in the user documentation. In determining 4410 the format and location of the safeguard, consideration will be given to the 4411 expected user group, the likelihood of contact and the likely nature of the injury 4412 arising. 4413
– 127 – 108/757/DC 9.6 Requirements for wireless power transmitters 4414
Rationale: Transmitters for near-field wireless power transfer can warm up foreign 4415 metallic objects that may be placed close to or on such a transmitter. To avoid 4416 burn due to high temperatures of the foreign metallic objects, the transmitter is 4417 tested as specified in 9.6.3. 4418
Far-field transmitters are generally called "power-beaming" and are not covered 4419 by these requirements. 4420
9.6.3 Test method and compliance criteria 4421
Rationale: While 9.6.3 specifies a maximum temperature of 70 °C, aluminum foil that 4422 reaches 80 °C is considered to comply with the requirement. The foil described 4423 in Figure 51 complies with the method allowed in in 9.3.1 based on the foil 4424 dimensions and low mass. 4425
This requirement is expected to align with the current Qi standard. 4426
Rationale: While many devices (servers, laptops, etc.) may be evaluated accurately for 4427 thermal burn injury using Table 38, foreign objects (FO’s) and other similar 4428 devices with low thermal mass and finite heat flux cannot be evaluated for 4429 thermal burn injury accurately. 4430
Both the experimental (thermesthesiometer method) and the computational (bio-4431 heat equation model) in conjunction with the thermal burn thresholds from ASTM 4432 C 1055 provide for a greater level of accuracy than IEC Guide 117 in assessing 4433 the potential risk for thermal burn injury from foreign objects by: 4434
− representing temperatures of the skin; 4435
− being material and geometry agnostic and; 4436
− considering quality of contact. 4437
Both methods take into account conservative assumptions that build in a margin 4438 of safety: 4439
− single finger (typically, finger and thumb would be used to pick up object); 4440
− no perfusion; 4441
− children/elderly reaction times; and 4442
− full thickness burn thresholds (vs +10˚C to obtain TS2). 4443
However, the findings from the experimental thermesthesiometer testing are 4444 being recommended due to the simplicity of the test method and to further 4445 promote future hazard-based testing using the thermesthesiometer. 4446
Generally, for a transmitter with a symmetrical single coil, the typical position 4447 (location) are the center, the edge and the midpoint of the coil of the transmitter. 4448 For a transmitter with an irregular shape coil or multiple coils, the typical position 4449 (location) where foreign objects should be placed can be determined by checking 4450 the structure or accompanying documents. See Figure 45 for some examples of 4451 single coils. 4452
4453
Figure 45 – Examples of symmetrical single coils 4454
– 128 – 108/757/DC
____________ 4455
10 Radiation 4456
10.2 Radiation energy source classifications 4457
Rationale: The first step in application is determining which energy sources represent 4458 potential radiation energy sources. Each energy source within the product can 4459 be classified as a radiation source based on the available energy within a circuit 4460 that can be used to determine the type of and number of safeguards required. 4461 The radiation energy source classifications include electromagnetic radiation 4462 energy sources. 4463
10.2.1 General classification 4464
Rationale: Radiation energy source classifications for X-rays and acoustics are given in 4465 Table 39. For optical radiation (“Lasers” and “Lamps and lamp systems”), the 4466 classification is defined by the IEC 60825 series or the IEC 62471 series as 4467 applicable. 4468
The general classification scheme specified in IEC 60825-1 is for laser products 4469 and is not a classification scheme for energy sources. It is not practical to classify 4470 laser radiation as RS. The classification according to IEC 60825-1 is used 4471 without modification. 4472
The classification schemes given in IEC 62471 and IEC 62471-5 specify a 4473 measurement distance (200 mm other than lamps intended for general lighting 4474 service and 1m for Image projectors) for the determination of the Risk Group. 4475 The Risk Group classification is not the actual source of the light. It is not 4476 practical to classify the radiation from lamps and lamp systems as RS. The 4477 classification according to IEC 62471 is used without modification. 4478
Abnormal operating conditions (see Clause B.3) and single fault conditions 4479 (see Clause B.4) need to be taken into account. If it becomes higher risk group 4480 when abnormal operating condition or single fault condition is applied, the 4481 higher risk group is applied for classification. 4482
Laser equipment classified as Class 1C is generally not within the scope of this 4483 document as it mainly applies to medical related applications. 4484
4485
– 129 – 108/757/DC
Source: IEC 60825-1:2014 and IEC 62471-5 4486
Rationale: Image Projectors are evaluated using the process in Figure 46 in this 4487 document (see IEC 60825-1:2014 and IEC 62471-5). 4488
4489
Figure 46 – Flowchart for evaluation of Image projectors (beamers) 4490
10.2.2 & 10.2.3 RS1 and RS2 4491
Rationale: The output circuits of personal music players are not subject to single fault 4492 conditions, since the outputs will not increase to a level exceeding RS2 by 4493 nature of their highly integrated hardware designs. Typically, when component 4494 faults are introduced during testing (by bypassing or shorting of the audio related 4495 ICs), the outputs are either shut down, reduced in level or muted. 4496
10.2.4 RS3 4497
Rationale: RS3 energy sources are those that are not otherwise classified as RS1 or RS2. 4498 No classification testing is required as these energy sources can have unlimited 4499 levels. If an energy source is not measured, it assumed to be RS3 for application 4500 of the document. A skilled person uses personal protective equipment or 4501 measures to reduce the exposure to safe limits when working where RS3 may 4502 be present. 4503
– 130 – 108/757/DC 10.3 Safeguards against laser radiation 4504
Source: IEC 60825-1:2014, Annex A 4505
Rationale: IEC 60825-1:2014, Annex A provides an explanation of the different classes of 4506 products. Accessible emission limits (AELs) are generally derived from the 4507 maximum permissible exposures (MPEs). MPEs have been included in this 4508 informative annex to provide manufacturers with additional information that can 4509 assist in evaluating the safety aspects related to the intended use of their 4510 product, such as the determination of the nominal ocular hazard distance 4511 (NOHD). 4512
10.4 Safeguards against optical radiation from lamps and lamp systems (including 4513 LED types) 4514
Source: IEC 62471 and IEC TR 62471-2 4515
Rationale: Excessive optical radiation may damage the retina and cause vision impairment 4516 or blindness. The limits in the referenced documents are designed to reduce the 4517 likelihood of vision impairment due to optical radiation sources. 4518
For the Instructional safeguard for lamps and lamp systems, see IEC 4519 TR 62471-2. 4520
10.4.1 General Requirements 4521
Source: IEC 60065 4522
Rationale: The term ‘Electronic light effect equipment’ has been used in IEC 60065 (see 4523 1.1) and is a commonly understood term for entertainment/stage effect lighting. 4524
10.5 Safeguards against X-radiation 4525
Source: IEC 60950-1; IEC 60065 4526
Rationale: Exposure to X-radiation will cause injury with excessive exposure over time. The 4527 limits in this document have been selected from IEC 60950-1 and IEC 60065 in 4528 order to limit exposure to that which is below harmful levels. 4529
10.6 Safeguards against acoustic energy sources 4530
Source: EN 60065:2002/A11:2008 4531
Rationale: The requirements of this subclause are made to protect against hearing loss due 4532 to long term exposure to high sound pressure levels. Therefore, the 4533 requirements are currently restricted to those kinds of products that are 4534 designed to be body-worn (of a size suitable to be carried in a clothing pocket) 4535 such that a user can take it with them all day long to listen to music (for example, 4536 on a street, in a subway, at an airport, etc.). 4537
At this moment, the clause does not contain requirements against the hazard of 4538 short term exposure to very high sound pressure levels. 4539
Rationale: Significance of LAeq,T in EN 50332-1 and additional information 4540
LAeq,T is derived from the general formula for equivalent sound pressure: 4541
4542
– 131 – 108/757/DC
This can be represented graphically as given in Figure 47 in this document. 4543
4544
Figure 47 – Graphical representation of LAeq,T 4545
In EN 50332-1 the measurement time interval (t2 – t1) is 30 s. 4546
In practice, and for the purposes of listening to personal music player content, 4547 LAeq,T has a time interval T (t2 – t1) in the order of minutes / hours and not 4548
seconds. 4549
Subclause 6.5 (Limitation value) of EN 50332-1:2000 acknowledges this fact and 4550 states that the 100-dB limit equates to a long time average of 90 dB LAeq,T. By 4551
using the IEC 60268-1 “programme simulation noise” test signal, this also takes 4552 the spectral content into account. 4553
The SCENHIR report states that 80 dB(A) is considered safe for an exposure 4554 time of 40 h/week. Most persons do not listen to 40 h/week to their personal 4555 music player. In addition, not all music tracks are at the same level of the 4556 simulated noise signal. Whilst modern music tends to be at around the same 4557 level, most of the available music is at a lower average level. Therefore, CLC TC 4558 108/WG03 considered a value of 85 dB(A) to be safe for an overwhelming 4559 majority of the users of personal music players. 4560
10.6.3 Requirements for dose-based systems 4561
Rationale: The requirements on dose measurement have been developed to replace the 4562 requirements on maximum exposure as this better protects against hearing 4563 damage, which results from the combination of exposure and time (dose). For 4564 now, both systems can be used. See Table 16 in this document for a 4565 comparison. 4566
– 132 – 108/757/DC
The dose-based system mainly uses the expression CSD, meaning "calculated 4567 sound dose". The value is based on the values mentioned in the EU Commission 4568 Decision 2009/490/EC, which stipulated that sound is safe when below 80 dB(A) 4569 for a maximum of 40 h per week. Therefore, the value of 100 % CSD corresponds 4570 to 80 dB(A) for 40 h. This also means that the safe limit in the dose measurement 4571 system is chosen to be lower than the safe limit in the maximum exposure 4572 system, as this specifies the safe limit at 85 dB(A). Consequently, a user will 4573 normally receive warnings earlier with the dose measurement system compared 4574 to the maximum exposure limit. In the maximum exposure system, the warning 4575 only had to be given once every 20 h of listening when exceeding 85 dB(A). In 4576 the dose measurement system, the warning and acknowledgement has to be 4577 repeated at least at every 100 % increase of the dose. In practice, this means 4578 that the warning is repeated at a comparable level of 83 dB(A), meaning a dose 4579 that corresponds to listening to 83 dB(A) for 40 h. At each next 100 % increase 4580 of dose level, the increase in corresponding dB’s is halved. Manufacturers have 4581 the freedom to give warnings earlier or ask for acknowledgement more 4582 frequently, but it has to be no later than at the next 100 % CSD increase since 4583 the last acknowledgement. For example, a device has provided the warning and 4584 acknowledgement at 100 % CSD. The manufacturer may choose to provide the 4585 next warning before 200 % CSD, for example, at 175 % CSD. If that is done, the 4586 next warning and acknowledgement may not be later than at 4587 275 % CSD. While there are no requirements for manufacturers to warn users 4588 before the 100 % CSD is reached, it is allowed to do so. Even more, it was felt 4589 by the document writers that it would be responsible behaviour if manufacturers 4590 warn consumers about the risks before the 100 % CSD level is reached. With 4591 the maximum exposure measurement, the maximum allowable sound output is 4592 100 dB(A). With the dosage system, only a momentary exposure limit (MEL) is 4593 required when exceeding 100 dB(A) if a visual or audible warning is provided. 4594 Where a visual or audible MEL is not provided the maximum exposure 4595 measurement of 100 dB(A) is required. 4596
An essential element to educating the user and promoting safe listening habits 4597 is appropriate and useful guidance. This can be accomplished with informative 4598 CSD and MEL warnings that allow the user to understand the hazard, risks, and 4599 recommended action. Appropriate warnings about using the device and user 4600 instructions shall be provided. It should be noted that the CSD warning can be 4601 provided in various forms not limited to visual or audio. However, the MEL can 4602 only be provided visually or audibly. Consideration should be given to not over-4603 message and annoy the user to the point where the message is neglected or 4604 evasive attempts (software hacks) to defeat the safe guards are taken. Extreme 4605 care should be given when implementing the MEL warning and shall be at the 4606 discretion of the manufacturer. 4607
Manufacturers should be aware that digital sensitivity between PMP and 4608 unknown listening devices may result in excessive false positives. It is 4609 recommended industry to promote sharing of sensitivity data through a 4610 standardized means. 4611
– 133 – 108/757/DC
Table 16 – Overview of requirements for dose-based systems 4612
Devices with Visual or Audible MEL EN 50332-
3
SPL
before transition3
SPL
after transition3
Dose
requirements
Dose
test method
Analog known 1
> 85 dB(A) if ack,
< 100 dB(A) max
<80 dB(A) max
CSD warn at every 100 %
MEL warn at >100 dB(A)
cl 5.2
Analog unknown 2
> 27 mV r.m.s. if ack,
< 150 mV r.m.s. max
< 15 mV rms max
CSD warn at every 100 % (= integrate. rms level 15 mV)
MEL warn at > 150 mV r.m.s.
cl 5.3
Digital known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
MEL warn at > 100 dB(A)
cl 5.2
Digital unknown 2
> -25 dBFS if ack,
< 100 dB(A)4 max
< -30 dBFS max
CSD warn at every 100 % (= integrate level -30 dBFS)
< 100 dB(A) max or MEL warn at > 100 dB(A)4
TBD 5
Devices without MEL EN 50332-
3
SPL
before transition3
SPL
after transition3
Dose
requirements
Dose
test method
Analog known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
< 100 dB(A) max
cl 5.2
Analog unknown 2
> 27 mV r.m.s. if ack,
< 150 mV r.m.s. max
< 15 mV r.m.s. max
CSD warn at every 100 % (= integrate rms level 15 mV)
< 150 mV r.m.s. max
cl 5.3
Digital known 1
> 85 dB(A) if ack,
< 100 dB(A) max
< 80 dB(A) max
CSD warn at every 100 %
< 100 dB(A) max
cl. 5.2
Digital unknown 2
> -25 dBFS if ack,
< 100 dB(A)4 max
< -30 dBFS max
CSD warn at every 100 % (= integrate level -30 dBFS)
< 100 dB(A)4 max
TBD 5
1 PMP includes or can detect listening device 2 PMP cannot detect listening device 3 Transition period allows migration to CSD before becoming mandatory 4 Defaults to 100 dB(A) gain cap from digital listening device. Need to develop industry wide protocol
for digital (wired/wireless) listening device for PMPs to learn sensitivity lookup table. 5 Need to create test requirements with EN 50332-3. Otherwise, SPL requirements (30 dBFS gain
cap) will be only feasible option.
4613
– 134 – 108/757/DC 10.6.6.1 Corded listening devices with analogue input 4614
Rationale: The value of 94 dB(A) was chosen to align with current practice in EN 50332. In 4615 addition, some equipment may already start clipping at 100 dB(A). The value 4616 used does not influence the result of the measurement. 4617
_____________ 4618
Annex A Examples of equipment within the scope of this standard 4619
Rationale: A variety of personal electronic entertainment products/systems can be covered 4620 by this document, including self-propelling types sometimes known as 4621 entertainment robots, which typically contain electronic components and circuits 4622 that power the device's motion, a battery system and charger, the electric 4623 motor(s) and control systems, together with wireless communications and audio. 4624 When no other IEC or ISO document explicitly covers these products, they can 4625 be accommodated by IEC 62368-1. 4626
Examples of Entertainment-type Robots: 4627
4628
____________ 4629
Annex B Normal operating condition tests, abnormal operating condition 4630 tests and single fault condition tests 4631
General Equipment safeguards during various operating conditions 4632
Purpose: To identify the various operating and use conditions of equipment that are taken into 4633 account in the document. This clause was proposed to be added to the document as 4634 a Clause 0.12, but was agreed to be added to the Rationale instead. 4635
Rationale: Operating conditions 4636
Normal operating condition – A normal operating condition is a state with 4637 intended functionality of the equipment. All equipment basic safeguards, 4638 supplementary safeguards, and reinforced safeguards remain effective and 4639 comply with all required safeguard parameters. 4640
Abnormal operating condition – An abnormal operating condition is a temporary 4641 state. The equipment may have full, limited, or no functionality. The equipment 4642 generally requires operator intervention for restoration to normal operating 4643 condition. All equipment basic safeguards remain effective but may not need to 4644 comply with the required safeguard parameters. All equipment supplementary 4645 safeguards and reinforced safeguards remain effective and comply with the 4646 required safeguard parameters. 4647
– 135 – 108/757/DC
Upon restoration of normal operating conditions, all basic safeguards comply 4648 with the required parameters unless the abnormal operating condition leads to a 4649 single fault condition, in which case the requirements for single fault condition 4650 apply. 4651
Reasonably foreseeable misuse condition – Reasonably foreseeable misuse is 4652 a form of an abnormal operating condition but may be either a temporary or a 4653 permanent state. The equipment may have full, limited, or no functionality. The 4654 equipment may not be capable of restoration to a normal operating condition. 4655 Reasonably foreseeable misuse may lead to a single fault condition, in which 4656 case equipment basic safeguards are not required to remain effective. All 4657 equipment supplementary safeguards and reinforced safeguards remain 4658 effective and comply with the required safeguard parameters. 4659
Other misuse condition – Other misuse (unreasonable or unforeseeable) may lead 4660 to a single or multiple fault condition, in which basic safeguards, supplementary 4661 safeguards and reinforced safeguards may not remain effective. The equipment 4662 may not be repairable to a normal operating condition. Safeguards against 4663 unreasonable or unforeseeable misuse are not covered by this document. 4664
Single fault condition – A single fault condition is a component or safeguard 4665 fault. The equipment may have full, limited or no functionality. The equipment 4666 requires repair to return to a normal operating condition. Equipment basic 4667 safeguards are not required to be functional, in this case the supplementary 4668 safeguards are functional and comply with the required safeguard parameters; or 4669 equipment supplementary safeguards are not required to be functional, in this case 4670 the basic safeguards are functional and comply with the required safeguard 4671 parameters. 4672
NOTE As a basic safeguard and a supplementary safeguard may be interchangeable, the concept 4673 of which safeguard is not required to remain effective can be reversed. 4674
B.1.5 Temperature measurement conditions 4675
Source: IEC 60950-1 4676
Purpose: To determine whether the steady state temperature of a part or material does or 4677 does not exceed the temperature limit for that part or material. 4678
Rationale: Steady state is considered to exist if the temperature rise does not exceed 3 K in 30 4679 min. If the measured temperature is less than the required temperature limit minus 4680 10 %, steady state is considered to exist if the temperature rise does not exceed 4681 1 K in 5 min. 4682
Temperature rise follows an exponential curve and asymptotically approaches 4683 thermal equilibrium. The rate of temperature rise can be plotted as a function of time 4684 and used to guess the value at steady state. The actual steady state value needs to 4685 be accurate only to the extent to prove whether the value will exceed the limit or not. 4686
Steady-state conditions of typical electronic devices have many different 4687 temperatures, so thermal equilibrium does not exist. 4688
The resistance method may be used to measure temperature rises of windings 4689 unless the windings are non-uniform or if it is difficult to make the necessary 4690 connections, in which case the temperature rise is determined by other means. 4691
When the resistance method is used, the temperature rise of a winding is calculated 4692 from the formula: 4693
Δt = 1
12R
RR − (k + t1) – (t2 – t1) 4694
where: 4695 Δt is the temperature rise of the winding; 4696 R1 is the resistance at the beginning of the test; 4697
R2 is the resistance at the end of the test; 4698
– 136 – 108/757/DC
k is equal to: 4699
• 225 for aluminium windings and copper/aluminium windings with an 4700 aluminium content ≥ 85 %, 4701
• 229,75 for copper/aluminium windings with a copper content > 15 % to < 4702 85 %, 4703
• 234,5 for copper windings and copper/aluminium windings with an 4704 copper content ≥ 85 %; 4705
t1 is the room temperature at the beginning of the test; 4706
t2 is the room temperature at the end of the test. 4707
NOTE It is recommended that the resistance of windings at the end of the test be determined by taking 4708 resistance measurements as soon as possible after switching off and then at short intervals so that a 4709 curve of resistance against time can be plotted for ascertaining the resistance at the instant of switching 4710 off. 4711
B.1.6 Specific output conditions 4712
Examples For example, connecting the intended representative worst-case load or external 4713 powered devices, and repeating with the appropriate resistive load and/or fault 4714 conditions. This is critical for determining characteristics such as output voltage and 4715 current for ES and PS classifications, use on building and other wiring, Annex Q, as 4716 well as proper loading for heating tests. These examples are not necessarily all 4717 inclusive. 4718
B.2.3 Supply Voltage 4719
Rationale: Where a test subclause does not require the most unfavourable supply voltage, the 4720 supply voltage is the value of the rated voltage or any value in the rated voltage 4721 range. This is applicable to the tests in abnormal operation condition and single 4722 fault condition as well. 4723
4724
Table 17 – Overview of supply voltage 4725
Requirement of IEC 62368-1:2020 Supply Voltage B.2.3
Normal operating conditions
Abnormal operating conditions and single
fault condition
5.2.2.2 Steady state voltage and current limits
5.7 Prospective touch voltage, touch current and protective conductor current
Including
Applies Applies
5.2.2.3 Capacitance limits
5.5.2.2 Capacitor discharge after disconnection of a connector
Does not apply Does not apply
5.2.2.4 Single pulse limits Applies Applies
5.2.2.5 Limits for repetitive pulses Applies Applies
5.2.2.7 Audio signals
E.1 Electrical energy source classification for audio signals
Does not apply Does not apply
5.4.1.8 Determination of working voltage Does not apply Does not apply
(short-circuit across the basic or supplementary
insulation)
5.7.4 Unearthed accessible parts Applies Applies
5.7.5 Earthed accessible conductive parts Applies Applies
5.7.6 Requirements when touch current exceeds ES2 limits
Applies Applies
– 137 – 108/757/DC
6.2.2 Power source circuit classifications Does not apply Does not apply
6.2.3 Classification of potential ignition sources Does not apply Does not apply
6.4 Safeguards against fire under single fault conditions
- Does not apply
8.2 Mechanical energy source classifications Does not apply Does not apply
9.2 Thermal energy source classifications Apply Does not apply
9.6 Requirements for wireless power transmitters Does not apply Does not apply
10.2 Radiation energy source classifications Does not apply Does not apply
Q.1 Limited power source Applies Applies
Q.2 Test for external circuits – paired conductor cable
Does not apply Does not apply
4726
B.2 – B.3 – B.4 Operating modes 4727
See Figure 48 in this document for an overview of operating modes. 4728
4729
Figure 48 – Overview of operating modes 4730
B.4.4 Functional insulation 4731
Rationale: The use of a functional insulation is only acceptable when the circuit does not 4732 exceed its limits of its class under normal operating conditions and abnormal 4733 operation conditions and single fault conditions of a component not serving as 4734 a safeguard (see 5.2.1.1 and 5.2.1.2). Otherwise a basic insulation/safeguard 4735 would be required. 4736
If the functional insulation possesses a certain quality (clearance, creepage 4737 distances, electric strength) comparable to a basic safeguard, it is acceptable to 4738 omit short-circuit. 4739
This cannot be compared to the short-circuiting of a basic safeguard as required in 4740 B.4.1, because this basic safeguard is a required one, while the added quality of 4741 the functional insulation is not required. 4742
If the short-circuiting of this functional insulation with added quality would lead to 4743 a changing of the class, the functional insulation was wrongly chosen, and a basic 4744 safeguard would have been required. 4745
– 138 – 108/757/DC B.4.8 Compliance criteria during and after single fault conditions 4746
Source: IEC 60065 4747
Rationale: During single fault conditions, short term power is delivered in components which 4748 might be outside the specifications for that component. As a result, the component 4749 might interrupt. During the interruption, sometimes a small flame escapes for a short 4750 period of time. The current practice in IEC 60065 allows these short term flames for 4751 a maximum period of 10 s. This method has been successfully used for products in 4752 the scope of this document for many years. 4753
____________ 4754
Annex C UV Radiation 4755
C.1.1 General 4756
Rationale: UV radiation can affect the physical properties of thermoplastic materials and so it 4757 can have a consequential effect on components protecting body parts from a range 4758 of injurious energy sources. 4759
____________ 4760
Annex D Test generators 4761
Source: ITU-T Recommendation K.44 4762
Rationale: The circuit 1 surge in Table D.1 is typical of voltages induced into telephone wires 4763 and coaxial cables in long outdoor cable runs due to lightning strikes to their earthing 4764 shield. 4765
The circuit 2 surge is typical of earth potential rises due to either lightning strikes to 4766 power lines or power line faults. 4767
The circuit 3 surge is typical of voltages induced into antenna system wiring due to 4768 nearby lightning strikes to earth. 4769
Figure D.3 provides a circuit diagram for high energy impulse to test the high-4770 pressure lamps. 4771
____________ 4772
Annex E Test conditions for equipment containing audio amplifiers 4773
Source: IEC 60065:2011 4774
Rationale: The proposed limits for touch voltages at terminals involving audio signals that 4775 may be contacted by persons have been extracted without deviation from 4776 IEC 60065:2011, 9.1.1.2 a). Under single fault conditions, 11.1 of 4777 IEC 60065:2011 does not permit an increase in acceptable touch voltage limits. 4778
The proposed limits are quantitatively larger than the accepted limits of Table 4, 4779 but are not considered dangerous for the following reasons: 4780
− the output is measured with the load disconnected (worst-case load); 4781
− defining the contact area of connectors and wiring is very difficult due to 4782 complex shapes. The area of contact is considered small due to the 4783 construction of the connectors; 4784
− normally, it is recommended to the user, in the instruction manual provided 4785 with the equipment, that all connections be made with the equipment in the 4786 “off” condition. 4787
– 139 – 108/757/DC
− in addition to being on, the equipment would have to be playing some program 4788 at a high output with the load disconnected to achieve the proposed limits. 4789 Although possible, it is highly unlikely. Historically, no known cases of injury 4790 have been recorded for amplifiers with a non-clipped output less than 71 V 4791 RMS. 4792
− the National Electrical Code (USA) permits accessible terminals with a 4793 maximum output voltage of 120 V RMS. 4794
It seems that the current normal condition specified in IEC 60065 is appropriate 4795 and a load of 1/8 of the non-clipped output power should be applied to the 4796 multichannel by adjusting the individual channels. 4797
___________ 4798
Annex F Equipment markings, instructions, and instructional safeguards 4799
F.3 Equipment markings 4800
Source: EC Directives such as 98/37/EC Machinery Directive, Annex I, clause 1.7.3 marking; 4801 NFPA 79:2002, clause 17.4 nameplate data; CSA C22.1 Canadian Electric Code, 4802 clause 2-100 marking of equipment give organized requirements. The requirements 4803 here are principally taken from IEC 60065 and IEC 60950 series. 4804
F.3.3.2 Equipment without direct connection to mains 4805
Source: IEC 60950-1 4806
Purpose: To clarify that equipment powered by mains circuits, but not directly connected to 4807 the mains using standard plugs and connectors, need not have an electrical rating. 4808
Rationale: Only equipment that is directly connected to the mains supplied from the building 4809 installation needs to have an electrical rating that takes into account the full load 4810 that may be connected to the building supply outlet. For equipment that is daisy-4811 chained or involves a master-slave configuration, only the master unit or the first 4812 unit in the daisy chain needs to be marked. 4813
F.3.6.2 Equipment class marking 4814
Rationale: For compliance with EMC standards and regulations, more and more class II 4815 products are equipped with a functional earth connection. The latest version of the 4816 basic safety publication IEC 61140 allows this construction. On request of IEC TC 4817 108, IEC SC3C has developed a new symbol, which is now used in IEC 62368-1. 4818
Rationale: Equipment having a class II construction, but that is provided with a class I input 4819 connector with the internal earthing pin not connected is also considered to be a 4820 class II equipment with functional earth. The class I connector is used to provide a 4821 more robust connection means, which is considered to be a functional reason for the 4822 earth connection. 4823
F.4 Instructions 4824
Rationale: The dash requiring graphical symbols placed on the equipment and used as an 4825 instructional safeguard to be explained does not apply to symbols used for 4826 equipment classification (see F.3.6). 4827
Markings on the equipment are reproduced in the instruction manual. Any translation 4828 of the wording on the marking is suggested to be provided in the manual. 4829
F.5 Instructional safeguards 4830
Rationale: When a symbol is used, the triangle represents the words “Warning” or “Caution”. 4831 Therefore, when the symbol is used, there is no need to also use the words 4832 “Warning” or “Caution”. However, when only element 2 is used, the text needs to be 4833 preceded with the words. 4834
___________ 4835
– 140 – 108/757/DC
Annex G Components 4836
G.1 Switches 4837
Source: IEC 61058-1 4838
Rationale: A contact should not draw an arc that will cause pitting and damage to the contacts 4839 when switching off and should not weld when switching on if located in PS2 or PS3 4840 energy sources. A PS1 energy source is not considered to have enough energy to 4841 cause pitting and damage to the contacts. Both these actions (pitting and damage) 4842 may result in a lot of heating that may result in fire. There should be sufficient gap 4843 between the two contact points in the off position which should be equal to the 4844 reinforced clearance if the circuit is ES3 and basic clearance if the circuit is ES2 or 4845 ES1 (we may have an arcing PIS or resistive PIS in an ES1 circuit) in order to avoid 4846 shock and fire hazards. The contacts should not show wear and tear and pitting after 4847 tests simulating lifetime endurance; and overload tests and operate normally after 4848 such tests. 4849
G.2.1 Requirements 4850
Source: IEC 61810-1, for electromechanical relays controlling currents exceeding 0,2 A AC 4851 or DC, if the voltage across the open relay contacts exceeds 35 V peak AC or 24 V 4852 DC 4853
Rationale: A contact should not draw an arc that will cause pitting and damage to the contacts 4854 when switching off and should not weld when switching on if located in PS2 or PS3 4855 energy sources. A PS1 energy source is not considered to have enough energy to 4856 cause pitting and damage to the contacts. Both these actions (pitting and damage) 4857 may result in lot of heating that may result in fire. There should be sufficient gap 4858 between the two contact points in the off position which should be equal to the 4859 reinforced clearance if the circuit is ES3 and basic clearance if the circuit is ES2 or 4860 ES1 (we may have an arcing PIS or resistive PIS in an ES1 circuit) in order to avoid 4861 shock and fire hazards. The contacts should not show wear and tear and pitting after 4862 tests simulating lifetime endurance, and overload tests and operate normally after 4863 such tests. 4864
G.3.3 PTC thermistors 4865
Source: IEC 60730-1:2006 4866
Rationale: PTC thermistor for current limitation is always connected in series with the load to 4867 be protected. 4868
In a non-tripping stage, the source voltage is shared by the load impedance and the 4869 resistance of PTC thermistor (which is close to the zero-power resistance at 25 °C). 4870 In order to define the power dissipation of the PTC thermistor in this stage, the 4871 source voltage and the load impedance are also important parameters. 4872
In a tripping stage, the PTC thermistor heats up by itself and increases the resistance 4873 value to protect the circuit. The zero-power resistance at 25 °C is no longer related 4874 to the power dissipation of PTC thermistors in this stage. The power dissipation of 4875 PTC thermistor in this stage depends on factors such as mounting condition and 4876 ambient temperature. 4877
In either stage, some parameters other than the rated zero-power resistance at an 4878 ambient temperature of 25 °C are required to calculate the power dissipation of PTC 4879 thermistor. 4880
The tripping stage is more hazardous than the non-tripping stage because the 4881 temperature of the PTC thermistor in the tripping stage becomes much higher than 4882 in the non-tripping stage. 4883
Figure 49 in this document shows “Voltage-Current Characteristics”. The blue dotted 4884 lines show the constant power dissipation line. It shows that the power at the 4885 operation point, during the tripping stage, is the highest power dissipation. This 4886 point is calculable with “Ires x Umax” of IEC 60738-1:2006, 3.38. 4887
– 141 – 108/757/DC
(Umax = maximum voltage, Ires = residual current, measured by the PTC 4888
manufacturers.) 4889
4890
4891
Figure 49 – Voltage-current characteristics (Typical data) 4892
If the PTC is installed in a PS1 circuit, the power dissipation of the PTC will be 4893 15W or less. In this state, the PTC is not considered to be a resistive PIS, 4894 regardless of its Ires x Umax. 4895
A PTC with a size of less than 1 750 mm3 is not considered to be a resistive 4896 PIS, described in 6.3.1, 6.4.5.2 and 6.4.6. 4897
G.3.4 Overcurrent protective devices 4898
Rationale: Just like any other safety critical component, protective devices are not allowed 4899 to be used outside their specifications, to guarantee safe and controlled 4900 interruption (no fire and explosion phenomena’s) during single fault 4901 conditions (short circuits and overload conditions) in the end products. This 4902 should include having a breaking capacity capable of interrupting the maximum 4903 fault current (including short-circuit current and earth fault current) that can 4904 occur. 4905
G.3.5 Safeguard components not mentioned in G.3.1 to G.3.4 4906
Rationale: Protective devices shall have adequate ratings, including breaking capacity. 4907
– 142 – 108/757/DC G.5.1 Wire insulation in wound components 4908
Source: IEC 60317 series, IEC 60950-1 4909
Purpose: Enamel winding wire is acceptable as basic insulation between external circuit 4910 at ES2 voltage level and an ES1. 4911
Rationale: ES1 becomes ES2 under single fault conditions. The enamel winding wires 4912 have been used in telecom transformers for the past 25 years to provide basic 4913 insulation between TNV and SELV. The winding wire is type tested for electric 4914 strength for basic insulation in addition to compliance with IEC 60317 series of 4915 standards. Enamel is present on both input and output winding wires and 4916 therefore, the possibility of having pinholes aligned is minimized. The finished 4917 component is tested for routine test for the applicable electric strength test 4918 voltage. 4919
G.5.2 Endurance test 4920
Source: IEC 60065:2011, 8.18 4921
Rationale: This test is meant to determine if insulated winding wires without additional 4922 interleaved insulation will isolate for their expected lifetime. The endurance test 4923 comprises a heat run test, a vibration test and a humidity test. After those tests, 4924 the component still has to be able to pass the electric strength test. 4925
G.5.2.2 Heat run test 4926
Rationale: In Table G.2, the tolerance is ± 5 °C. It is proposed that the above tolerance be 4927 the same. 4928
G.5.3 Transformers 4929
Source: IEC 61558-1, IEC 60950-1 4930
Rationale: Alternative requirements have been successfully used with products in the scope 4931 of this document for many years. 4932
G.5.3.3 Transformer overload tests 4933
G.5.3.3.2 Compliance criteria 4934
Source: IEC 61558-1, IEC 60950-1 4935
Rationale: The transformer overload test is conducted mainly to check the deterioration by 4936 thermal stress due to overload conditions, and the compliance criteria is to check 4937 whether the temperature of the windings are within the allowable limits specified 4938 in Table G.3. For that purpose, the maximum temperature of windings is 4939 measured. 4940
However, in the actual testing condition, the windings or other current carrying 4941 parts of the transformer under testing may pose temperature higher than the 4942 measured value due to uneven temperature, such as a windings isolated from 4943 the mains (see third paragraph of G.5.3.3.2), so that such spot exposed to higher 4944 temperature may have thermal damage. 4945
In order to evaluate such potential damage, electric strength test after the 4946 overload condition is considered necessary. 4947
Both of the source documents require the electric strength test after the overload 4948 test. 4949
Table G.3 Temperature limits for transformer windings and for motor windings (except 4950 for the motor running overload test) 4951
Although the document does not clearly state it, the first row should also be used 4952 in cases where no protective device is used or the component is inherently 4953 protected by impedance. 4954
– 143 – 108/757/DC
For example, in the test practice of a switch mode power supply, a transformer 4955 is to be intentionally loaded to the maximum current without a protection 4956 operating. In this case, the method of protection is NOT ‘inherently’ or 4957 ‘impedance’, but other sets of limits are specified with the time of protection to 4958 operate. In reality, a switch mode transformer tested with a maximum load 4959 attempting the protection not to operate, but the limits in first row have been 4960 considered appropriate, because the thermal stress in that loading condition 4961 continues for a long time (no ending). Thus, the lowest limit should be applied. 4962 In this context, the application of the first row limit shall be chosen according to 4963 the situation of long lasting overloading rather than the type of protection. 4964
G.5.3.4 Transformers using fully insulated winding wire (FIW) 4965
Source: IEC 60317-56, IEC 60317-0-7 4966
Rationale: In 2012, IEC TC 55 published IEC 60317-56 and IEC 60317-0-7, Specification 4967 for Particular Types of Winding Wires – Part 0-7: General requirements – Fully 4968 insulated (FIW) zero-defect enamelled round copper wire with nominal conductor 4969 diameter of 0,040 mm to 1,600 mm. 4970
This wire is more robust enameled-coated wire used with minimal amounts of 4971 interleaved insulation. It is another step in the advancement of technology to 4972 allow manufacturers to design smaller products safely. 4973
IEC TC 96 was the first TC to incorporate the use of FIW in their safety 4974 documents for switch mode power supply units, IEC 61558-2-16. Since G.5.3.1 4975 references IEC 61558-1-16 as one of the acceptable documents for transformers 4976 used in switch mode power supplies, FIW already is acceptable in equipment 4977 investigated to IEC 62368-1 that use an IEC 61558-1-16 compliant transformer. 4978
FIW may not be accessible, whether it has basic insulation, double insulation 4979 or reinforced insulation. Note that this differs from other parts of the document 4980 that permit supplementary insulation and reinforced insulation to be 4981 accessible to an ordinary person. The reason is that this kind of wire is fragile 4982 and the insulation could easily be damaged when it is accessible to an ordinary 4983 person. 4984
G.5.4 Motors 4985
Source: IEC 60950-1 4986
Rationale: Requirements have been successfully used with products in the scope of this 4987 document for many years. 4988
G.7 Mains supply cords 4989
Source: IEC 60245 (rubber insulation), IEC 60227 (PVC insulation), IEC 60364-5-54 4990
Rationale: Mains connections generally have large normal and fault energy available from 4991 the mains circuits. It is also necessary to ensure compatibility with installation 4992 requirements. 4993
Stress on mains terminal that can result in an ignition source owing to lose or 4994 broken connections shall be minimized. 4995
Terminal size and construction requirements are necessary to ensure adequate 4996 current-carrying capacity and reliable connection such that the possibility of 4997 ignition is reduced. 4998
Wiring flammability is necessary to reduce flame propagation potential should 4999 ignition take place. 5000
Conductor size requirements are necessary to ensure adequate current-carrying 5001 capacity and reliable connection such that the possibility of ignition is reduced. 5002
– 144 – 108/757/DC Alternative cords to rubber and PVC are accepted to allow for PVC free 5003
alternatives to be used. At the time of development of the document, IEC TC20 5004 had no published documents available for these alternatives. However, several 5005 countries do have established requirements. Therefore, it was felt that these 5006 alternatives should be allowed. 5007
G.7.3 – G.7.5 Mains supply cord anchorage, cord entry, bend protection 5008
Source: IEC 60065:2011 and IEC 60950-1:2013 5009
Purpose: Robustness requirements for cord anchorages 5010
Rationale: The requirements for cord anchorages, cord entry, bend protection and cord 5011 replacement are primarily based on 16.5 and 16.6 of IEC 60065:2011 and 3.2.6 5012 and 3.2.7 of IEC 60950-1:2013. 5013
Experience shows that 2 mm displacement is the requirement and if an 5014 appropriate strain relief is used there is no damage to the cord and therefore, no 5015 need to conduct an electric strength test in most cases. This method has been 5016 successfully used for products in the scope of these documents for many years. 5017
G.8 Varistors 5018
Source: IEC 61051-1 and IEC 61051-2 5019
Rationale: The magnitude of external transient overvoltage (mainly attributed to lightning), 5020 to which the equipment is exposed, depends on the location of the equipment. 5021
This idea is described in Table 14 of IEC 62368-1 and also specified in 5022 IEC 60664-1. 5023
In response to this idea, IEC 61051-2 has been revised taking into account the 5024 location of the equipment, which also influences the requirement for the varistors 5025 used in the equipment. 5026
The combination pulse test performed according to G.8.2 of IEC 62368-1 can 5027 now refer to the new IEC 61051-2 with Amendment 1. 5028
G.9 Integrated circuit (IC) current limiters 5029
Source: IEC 60730-1, IEC 60950-1 5030
Rationale: Integrated circuits (containing numerous integral components) are frequently 5031 used for class 1 and class 2 energy source isolation and, more frequently (for 5032 example, USB or PoE), for functions such as current limiting. 5033
IEC 60335 series already has requirements for “electronic protection devices,” 5034 where conditioning tests such as EMF impulses are applied to such ICs, and the 5035 energy source isolation or current limiting function is evaluated after conditioning 5036 tests. When such energy isolation or current limitation has been proven reliable 5037 via performance, pins on the IC associated with this energy isolation or limitation 5038 are not shorted. 5039
For ICs used for current limitation, two test programs were used in 5040 IEC 60950-1:2009. An additional program was developed in IEC 62368-1:2010. 5041 It was felt that all three programs were considered adequate. Therefore, the 5042 three methods were kept. 5043
An Ad Hoc formed at the March 2015, Northbrook HBSDT meeting revised this 5044 test program with the following guiding principles: 5045
a) Streamline the number of tests in overall test program to concentrate on 5046 those tests and conditions that most likely will identify deficiencies in IC 5047 Current Limiter design from a safety perspective, such as allowing more 5048 current to flow than designed for. Some of the existing conditions are 5049 redundant or have questionable value identifying such deficiencies. 5050
b) Focus on test conditions that are applicable for semiconductor devices 5051 rather than test conditions more suited for traditional electro-mechanical 5052
– 145 – 108/757/DC
devices. For example, 10 000-cycle testing has more applicability to 5053 electro-mechanical devices (in relation to parts wearing out) versus 5054 semiconductor devices (such as IC current limiters). 5055
c) Combine test conditions when justified to increase efficiency when 5056 conducting individual tests, also trying to make the testing more compatible 5057 with automated testing processes (for example, combine individual 5058 temperature tests as individual sub-conditions of other required tests). 5059
Table G.10 provides the specific performance test program for IC current 5060 limiters. 5061
− Input loading to the device should be representative of the manufacturer’s IC 5062 specification (as typically communicated in the IC application notes for the 5063 particular device). 5064
− Output loading is intended to represent a short circuit condition (0 Ω shunt), 5065 with parallel capacitive loading (470 µF +/- 20 %) to better accommodate 5066 on/off cycling. 5067
See Figure 50 in this document for additional detail. 5068
5069
Figure 50 – Example of IC current limiter circuit 5070
Regarding the 250 VA provision, this provision is intended to mean that the usual 5071 test power source has 250 VA capability as long as the IC is designed for 5072 installation in a system with a source of 250 VA or larger. If the power source 5073 capability is intended to be less than 250 VA, then the manufacturer must specify 5074 so, or test in the end product. Testing at 250 VA is intended to include 250 VA 5075 or larger sources because the test program is covering relatively small and low-5076 voltage silicon devices – if these devices pass at 250 VA they likely would pass 5077 at higher VA too since they are not electro-mechanical. Also, this allows for more 5078 practical associated certification test programs. 5079
Also, to avoid recertification of existing components, IC current limiters that met 5080 a previous legacy test program (G.9.2, G.9.3 or G.9.4) are an equivalent level of 5081 safety as the proposed rewritten Clause G.9, primarily because Clause G.9 is 5082 derivation of the legacy requirements. Therefore, IC current limiters that comply 5083 with the legacy test program should not need to be reinvestigated to the latest 5084 document that includes this revised Clause G.9. However, this is a certification 5085 consideration outside the scope of this technical committee. 5086
– 146 – 108/757/DC G.11 Capacitors and RC units 5087
Source: IEC 60384-14:2005 5088
Rationale: Table G.11: Test voltage values aligned with those used in IEC 60384-14 (Tables 5089 1, 2 and 10 of IEC 60384-14:2005). 5090
Table G.12: Minimum number of Y capacitors based on required withstand 5091 voltage of Table 25. 5092
Table G.13: Maximum voltage that can appear across a Y capacitor based on 5093 the peak value of the working voltage of Table 26. 5094
Table G.14: Minimum number of Y capacitors based on the test voltages (due to 5095 temporary overvoltages) of Table 27. 5096
Table G.15: Minimum number of X capacitors (line to line or line to neutral) based 5097 on the mains transient withstand voltage of Table 13. 5098
All of the above are aligned with the requirements of IEC 60384-14. 5099
G.13 Printed boards 5100
Source: IEC 60950-1 or IEC 60664-3:2003. 5101
Purpose: To provide details for reliable construction of PCBs. 5102
Rationale: This proposal is based on IEC 60664-3 and the work of IBM and UL in testing 5103 coatings on printed boards when using coatings to achieve insulation 5104 coordination of printed board assemblies. Breakdown voltages of more than 5105 8 000 V for 0,025 mm were routinely achieved in this program. 5106
These parts have multiple stresses on the materials with limited separation 5107 between conductors. This section is taken from IEC 60950-1, where these 5108 requirements have been used for many years. 5109
G.13.6 Tests on coated printed boards 5110
Purpose: Prevent breakdown of the insulation safeguard. 5111
Rationale: Avoid pinholes or bubbles in the coating or breakthrough of conductive tracks at 5112 corners. 5113
G.14 Coatings on component terminals 5114
Source: IEC 60950-1 and IEC 60664-3 5115
Purpose: The mechanical arrangement and rigidity of the terminations are adequate to 5116 ensure that, during normal handling, assembly into equipment and subsequent 5117 use, the terminations will not be subject to deformation which would crack the 5118 coating or reduce the separation distances between conductive parts. 5119
Rationale: The terminations are treated like coated printed boards (see G.13.3) and the 5120 same separation distances apply. 5121
This section is taken from IEC 60950-1 where these requirements have been 5122 used for many years. 5123
G.15 Pressurized liquid filled components 5124
Source: IEC 60065, IEC 60950-1, IEC 61010-1, UL 1995, UL 2178, ASHRAE TC9.9 & 5125 ASME B31 series and EU PED 5126
Purpose: Avoid spillage of liquids resulting in electric shock hazard 5127
Rationale: The requirements apply to products that use water cooling technologies. Section 5128 G.15.2 provides the requirements for self-contained devices, containing less 5129 than 1 l of liquid, and G.15.3 provides the requirements for modular. A leak in 5130 the system near a hazardous voltage, may result in a shock hazard and 5131 therefore, needs to be properly addressed. A leak is not desirable and therefore, 5132 a strict performance criterion is proposed. 5133
– 147 – 108/757/DC The decision flowchart illustrates and helps to explain demarcation points 5134
between self-contained and modular LFC systems and which requirements to 5135 apply. 5136
LFC Test Requirements
System contains Modular LFC?
Test According to G.15.2
YES
NO
Test According to G.15.3
5137
Figure 51 – Decision flowchart 5138
5139
Rationale: Additional considerations must be taken into account when incorporating 2-5140 phase refrigerants. Refrigerants are classified based on toxicity (first letter) and 5141 flammability (second/third number/letter). Refrigerant’s toxicity classification “A” 5142 is less hazardous than “B”. Likewise, Refrigerant flammability classifications “1”, 5143 “2L”, “2” and “3”, ranging from no flame propagation potential to higher 5144 flammability potential. For example, a refrigerant classified as “A1” is lower risk 5145 for toxicity and flammability than a “B2” refrigerant. 5146
European Union (EU) Pressure Equipment Directive (PED), 2014/68/EU, 5147 includes caveats for applicability of smaller systems that are low risk. 5148 Refrigeration systems having a pressure greater than 0.05 MPa (72.5 PSI) are 5149 considered to be assemblies falling within the scope of the PED. However, 5150 according to Article 1, item 2(f) of the directive, equipment classified no higher 5151 than Category I and covered by the low voltage directive is excluded from its 5152 scope. 5153
According to guidelines of the PED, this exclusion applies to both components 5154 and assemblies (refrigerant filled components). This applies to equipment 5155 containing vessels (for example, compressors, receivers) or piping with limits in 5156 accordance with the following (i.e. Category I limits for gases): 5157
− Vessels 5158
• dangerous refrigerants (Annex II, Table 1): 5159
− volume not exceeding 1 l, or 5160
− pressure x volume not exceeding 5 MPa 5161
• non-dangerous refrigerants (Annex II, Table 2): 5162
− volume not exceeding 1 l, or 5163
− pressure x volume not exceeding 20 MPa 5164
− Piping 5165
• dangerous refrigerants (Annex II, Table 6): 5166
− numerical designation not exceeding 25, or 5167
− pressure not exceeding 1 MPa and numerical designation not exceeding 100, 5168 or 5169
– 148 – 108/757/DC
− pressure exceeding 1 MPa and pressure x numerical designation not 5170 exceeding 100 MPa 5171
• non-dangerous refrigerants (Annex II, Table 7): 5172
− numerical designation not exceeding 100, or 5173
− pressure x numerical designation not exceeding 350 MPa. 5174
For other components, the most onerous limit of the two applies. The volume 5175 is the internal volume of the vessel and includes the volume of pipework up to 5176 the first connection. It excludes the volume of fixed internal parts. The pressure 5177 is the maximum pressure the vessel or piping system is exposed to, as specified 5178 by the manufacturer of the equipment. 5179
NOTE 1 The numerical designation (ND) designates the size common to all components in the 5180 piping system 5181
If any component exceeds the limits given above, the equipment has to also 5182 comply with the PED. The PED technical requirements are given in Annex I and 5183 the conformity assessment tables and procedures in Annexes II and III 5184 respectively. Other refrigeration standards may need to be consulted for large-5185 scale refrigeration systems (see below). 5186
NOTE 2 Large-scale refrigeration systems would include systems exceeding PED Category 1. 5187
Additional Refrigeration Standard References (not fully exhaustive): 5188
− IEC 60335-2-40:2018, Household and similar electrical appliances – Safety – 5189 Part 2-40: Particular requirements for electrical heat pumps, air-conditioners, 5190 and dehumidifiers 5191
− IEC 61010-011:2019, Safety requirements for electrical equipment for 5192 measurement, control, and laboratory use - Part 2-011: Particular 5193 requirements for refrigerating equipment 5194
− ASHRAE 15, Safety Standard for Refrigeration Systems 5195
− ASHRAE 34, Designation and Safety Classification of Refrigerants 5196
− IEC 60335-2-89, Household and similar electrical appliances – Safety – Part 5197 2-89: Particular requirements for commercial refrigerating appliances and ice-5198 makers with an incorporated or remote refrigerant unit or motor-compressor 5199
− ISO 5149 series, Refrigerating systems and heat pumps — Safety and 5200 environmental 5201
− requirements 5202
− ISO 817, Refrigerants - Designation and safety classification 5203
− UL 1995, Heating and Cooling Equipment (safety) 5204
− EN 378 series, Refrigerating systems and heat pumps. Safety and 5205 environmental requirements. 5206
− EN 13445 series, Unfired pressure vessels 5207
− EN 13480 series, Metallic industrial piping 5208
IEC 60335-2-40:2018, Annex EE specify pressure tests for refrigeration systems. 5209 The pressure tests value shall be at least 3x maximum allowable pressure 5210 developed during all of the following conditions: 5211
− Normal operation (Clause 11, Heating), 5212
− Abnormal operation (Clause 19), 5213
− Standstill Conditions (Annex EE.4) 5214
NOTE 3 Components that comply with the fatigue test in EE.5 can reduce pressure test to 2x 5215 maximum allowable pressure (67% of original test pressure). 5216
– 149 – 108/757/DC The test is carried out on 3 samples of each component. Pressure is raised 5217
gradually until test pressure is reached and then maintained for at least 1 minute. 5218 During the test, the samples shall not leak. 5219
NOTE 4 Where gaskets are employed for sealing samples, leakage in gaskets are acceptable, 5220 assuming the leakage occurs at a pressure greater than 120% of the maximum allowable pressure 5221 and test pressure is still reached for the specified time. 5222
G.15.2 Test methods and compliance criteria for self-contained LFC 5223
Self-Contained LFC System
Equipment enclosure
Cold PlatePump
CPU
Heat Exchanger (Radiator)
FANMotherboard
5224
Figure 52 – Illustration of a self-contained LFC system 5225
The requirements were developed based on the following description of a typical 5226 system using liquid filled heat sinks. If a different type of system is used, then 5227 the requirements need to be re-evaluated. 5228
Liquid filled heat-sink system (LFHS): a typical system consists of a heat 5229 exchanger, fan, pump, tubing, fittings and cold plate or radiator type heat 5230 exchanger. The liquid filled heat sink comes from the vendor already charged, 5231 sealed; and is installed and used inside the equipment (small type, typically 5232 found in cell stations and computing devices or other types of systems). The 5233 proposed requirements are based on a LFHS being internal to a unit, 5234 used/installed adjacent/over ES1 circuits, in proximity to an enclosed power 5235 supply (not open frame). 5236
The liquid-filled heat components are used in desktop units or stationary 5237 equipment and in printers. These are not used in any portable equipment where 5238 orientation may change (unless the product is tested in all such orientations. If 5239 the liquid heat sink system is of a sealed type construction, then the system is 5240 orientation proof (this should not be a concern but a good engineering practice 5241 is that the pump does not become the high point in the system). 5242
Following assumptions are used: 5243
– The tubing is a single-layered metal (copper or aluminium) or non-metallic 5244 construction. If it is non-metallic, flammability requirements will apply. 5245
– The fittings are metal. If it is non-metallic, flammability requirements will 5246 apply. 5247
– Working pressure is determined under normal operating conditions and 5248 abnormal operating conditions and construction (tubing, fitting, heat 5249 exchanger, any joints, etc.) is suitable for this working pressure; 5250
– The volume of the liquid is reasonable (less than 1 000 ml). 5251
– The fluid does not cause corrosion and is not flammable (for example, 5252 corrosion resistant and non-flammable liquid). 5253
– The liquid is non-toxic as specified for the fluid material. 5254
– 150 – 108/757/DC
G.15.3 Test methods and compliance criteria for a Modular LFC 5255
Modular LFC System
Chiller Distribution
Unit
Server
ManifoldServer Node
Cold PlateCPU
Motherboard
Server Node
Cold PlateCPU
Motherboard
5256
Figure 53 – Illustration of a modular LFC system 5257
G.15.3.1 Hydrostatic pressure test 5258
Rationale: Based on input from ASHRAE TC9.9, Data Center Networking Equipment use 5259 single-phase cooling systems (typically water/glycol mix or facility water) which 5260 should align with facility piping standards used in facility water systems. 5261
ASHRAE & ASME B31 Series standards: According to ASME B31.5 piping 5262 standard, the hydrostatic Pressure test for water-based coolants is 1.5x max 5263 design pressure or 50 psig whichever is greater. The test levels are based on 5264 maximum design pressure for the respective fluid loop. 5265
EU PED: According to the European pressure directive essential requirements, 5266 the hydrostatic test pressure for pressure vessels must be no less than 5267 corresponding to the maximum loading to which the pressure equipment may be 5268 subject in service taking into account its maximum allowable pressure and its 5269 maximum allowable temperature, multiplied by the coefficient 1,25, or the 5270 maximum allowable pressure multiplied by the coefficient 1,43, whichever is the 5271 greater. 5272
Hydrostatic test multipliers should be applied to maximum operating pressure 5273 under normal, abnormal, and single-fault conditions. This could be: 5274
− max rated pressure (from external source) 5275
− max pressure setting of overpressure safety device 5276
− max pressure generated within the device or assembly that is not relying on 5277 overpressure safety device 5278
NOTE For flammable, toxic, or corrosive liquids additional requirements may apply (e.g. other 5279 standards, local codes for HazLoc, etc.). 5280
Applicable standards that specify hydrostatic pressure strength type testing 5281 require a 1 min duration (e.g. IEC 61010-1, UL 1995, UL 2178,). These are 5282 proven/tested standards that the industry/test labs commonly use. 5283
– 151 – 108/757/DC
Rack System
CDU* (Max Pressure 100 PSI)
Server Rail (Max Pressure 100 PSI)
Server Rail (Max Pressure 150 PSI)
Server Rail (Max Pressure 80 PSI)
Self-Contained LFC < 1 liter(G.15)
Server Rail (Max Pressure 80 PSI)
Facility
Pressure Relief Valve (PRV) Set @
80 PSI
Manifold
Server Rail (Max Pressure 150 PSI)
Pressure Relief Valve (PRV) Set @
80 PSI
Server Rail (Max Pressure 100 PSI)
Manifold
Pressure Relief Valve (PRV) Set @
100 PSI
Server Rail (Max Pressure 100 PSI)
Facility Water System (Max Water Pressure 120PSI)
* NOTE: CDU’s may be rack mounted or free-standing. Smaller CDU’s (as shown) tend to be rackmounted, while larger CDU’s are free-standing equipment and tend to be outside the rack.
Supplementary Safeguard (to protect downstream LFC components)
Supplementary Safeguard (to protect downstream LFC components)
NOTE: During system level hydrostatic testing, PRV(s) are removed and piping blocked for testing upstream system elements. Depending on LFC’s max pressure ratings, hydrostatic pressure tests may need to be done in stages.
Example of Complete Modular Subsystem
5284
Figure 54 – Example illustration of a rack modular LFC subsystems with internal and 5285 external connections. 5286
Common ASHRAE TC 9.9 Acronym and Terms: 5287
− CDU – Coolant Distribution Unit 5288
− FWS – Facilities Water System 5289
− TCS – Technology Cooling System 5290
− RFU – Rack Filtration Unit 5291
− FFU – Facility Filtration Unit 5292
− Wetted materials/equipment – components/assemblies within the cooling 5293 system that may directly contact the coolant. 5294
– 152 – 108/757/DC
5295
Figure 55 – CDU Liquid Cooling System within a Data Center (courtesy of ASHRAE 5296 TC9.9) 5297
CoolingTower
Chiller
Datacom Equipment Center
Building
Rack Rack
ITE
RFU
ITE
FFU
Facilities Water System(FWS)
Condenser Water System(CWS) 5298
Figure 56 – Non-CDU Liquid Cooling System within Data Center (courtesy of ASHRAE 5299 TC9.9) 5300
5301
– 153 – 108/757/DC Explanation to why Vibration testing was not included for Modular LFC 5302
Vibration testing is not included in the requirements for large liquid cooled 5303 systems. Such testing is intended to simulate vibration occurring in 5304 transportation and during use. Generally, its use as a test discipline is more 5305 closely associated with the reliability and quality of the equipment/system than 5306 product safety. Furthermore, because such large liquid cooled systems will be 5307 subjected to hydrostatic pressure testing at 1.5 times maximum rated working 5308 pressure, it is expected that such hydrostatic pressure testing encompasses any 5309 deficiencies that might be discovered via vibration testing, and thus such large 5310 liquid cooled systems will not be further compromised due to vibration to a 5311 degree that equipment safeguards would be defeated. Finally, it is assumed that 5312 such large liquid cooled systems, by nature of being part of professional 5313 equipment, will be subject to onsite inspections during the equipment 5314 commissioning process to ensure that all systems and components, including 5315 liquid cooling, are functioning per the manufacturer’s operational requirements 5316 before use. 5317
G.15.3.6 Compliance Criteria 5318
Rationale: Final installation of the product if up to the final integrator. 100% leak free 5319 inspection is expected, no spill near hazardous voltage should happen. 5320
___________ 5321
Annex H Criteria for telephone ringing signals 5322
H.2 Method A 5323
Source: IEC 62949:2016. 5324
Rationale: Certain voltages within telecommunication networks often exceed the steady 5325 state, safe-to-touch limits set within general safety documents. Years of practical 5326 experience by world-wide network operators have found ringing and other 5327 operating voltages to be electrically safe. Records of accident statistics indicate 5328 that electrical injuries are not caused by operating voltages. 5329
Access to connectors carrying such signals with the standard test finger is 5330 permitted, provided that inadvertent access is unlikely. The likelihood of 5331 inadvertent access is limited by forbidding access with the test probe Figure 2C 5332 of IEC 60950-1:2013 that has a 6 mm radius tip. 5333
This requirement ensures that: 5334
– contact by a large part of the human body, such as the back of the hand, is 5335 impossible; 5336
– contact is possible only by deliberately inserting a small part of the body, 5337 less than 12 mm across, such as a fingertip, which presents a high 5338 impedance; 5339
– the possibility of being unable to let-go the part in contact does not arise. 5340
This applies both to contact with signals arriving from the network and to signals 5341 generated internally in the equipment, for example, ringing signals for extension 5342 telephones. By normal standards, these internally generated signals would 5343 exceed the voltage limits for accessible parts, but the first exemption in 5344 IEC 60950-1 states that limited access should be permitted under the above 5345 conditions. 5346
Ventricular fibrillation of the heart is considered to be the main cause of death 5347 by electric shock. The threshold of ventricular fibrillation (Curve A) is shown in 5348 Figure 57 in this document and is equivalent to curve c1 of IEC TS 60479-1:2005, 5349 Figure 14. The point 500 mA/100 ms has been found to correspond to a 5350 fibrillation probability of the order of 0,14 %. The let go limit (Curve B) is 5351 equivalent to curve 2 of IEC TS 60479-1:2005, Figure 14. Some experts consider 5352
– 154 – 108/757/DC
curve A to be the appropriate limit for safe design, but use of this curve is 5353 considered as an absolute limit. 5354
5355
Figure 57 – Current limit curves 5356
Contact with telecommunication operating voltages (EN 41003) 5357
Total body impedance consists of two parts, the internal body resistance of blood 5358 and tissue and the skin impedance. Telecommunication voltages hardly reach 5359 the level where skin impedance begins to rapidly decrease due to breakdown. 5360 The skin impedance is high at low voltages, its value varying widely. The effects 5361 of skin capacitance are negligible at ringing frequencies. 5362
IEC TS 60479-1 body impedance figures are based upon a relatively large 5363 contact area of 50 cm2 to 100 cm2, which is a realistic value for mains operated 5364 domestic appliances. Practical telecommunication contact is likely to be much 5365 less than this, typically 10 cm2 to 15 cm2 for uninsulated wiring pliers or similar 5366 tools and less than 1 cm2 for finger contact with pins of a telephone wall socket. 5367 For contact with thin wires, wiring tags or contact with tools where fingers move 5368 beyond insulated handles, the area of contact will again be of the order of 1 cm2 5369 or less. These much smaller areas of contact with the body produce significantly 5370 higher values of body impedance than the IEC TS 60479 figures. 5371
In IEC 60950-1, a body model value of 5 kΩ is used to provide a margin of safety 5372 compared with the higher practical values of body impedance for typical 5373 telecommunication contact areas. 5374
The curve B' [curve C1 of IEC TS 60479-1:2005, Figure 22 (curve A in this 5375
document)] used within the hazardous voltage definition is a version of curve B 5376 modified to cover practical situations, where the current limit is maintained 5377 constant at 16 mA above 1 667 ms. This 16 mA limit is still well within the 5378 minimum current value of curve A. 5379
The difficulties of defining conditions that will avoid circumstances that prevent 5380 let-go have led to a very restricted contact area being allowed. 5381
Contact with areas up to 10 cm2 can be justified and means of specifying this 5382 and still ensuring let-go are for further study. 5383
– 155 – 108/757/DC H.3 Method B 5384
Source: This method is based on USA CFR 47 ("FCC Rules") Part 68, Sub part D, with 5385 additional requirements that apply under fault conditions. 5386
___________ 5387
Annex J Insulated winding wires for use without interleaved insulation 5388
Source: IEC 60851-3:2009, IEC 60851-5:2008, IEC 60851-6:1996 5389
Purpose: Winding wires shall withstand mechanical, thermal and electrical stress during 5390 use and manufacturing. 5391
Rationale: Test data indicates that there is not a major difference between rectangular wires 5392 and round wires for electric strength after the bend tests. Therefore, there is no 5393 reason to not include them. 5394
Subclause 4.4.1 of IEC 60851-5:2008 covers only solid circular or stranded 5395 winding wires as a twisted pair can easily be formed from round wires. It is 5396 difficult to form a twisted pair from square or rectangular winding wires. 5397
IEC 60851-5:2008, 4.7 addresses a test method that can be used for square and 5398 rectangular wires. A separate test method for square and rectangular wires has 5399 been added. The test voltage is chosen to be half of the twisted pair as a single 5400 conductor is used for the testing. 5401
In addition, the edgewise bend test is not required by IEC 60851-5 and 5402 IEC 60851-6 for the rectangular and square winding wires. 5403
The reference to trichloroethane is being deleted as trichloroethane is an 5404 environmentally hazardous substance. 5405
For J.2.3 (Flexibility and adherence) and J.2.4 (Heat shock), 5.1.2 in Test 8 of 5406 IEC 60851-3:2009 and 3.2.1 of IEC 60851-6:1996 are not used for solid square 5407 and solid rectangular winding wires. 5408
___________ 5409
Annex K Safety interlocks 5410
Source: IEC 60950-1 5411
Purpose: To provide reliable means of safety interlock devices. 5412
Rationale: Safety interlock constructions have been used for many years in products within 5413 the scope of this document. Safety interlocks should not be associated with 5414 electro-mechanical components only. 5415
K.7.1 Safety interlocks 5416
Source: IEC 60950-1 5417
Purpose: To provide reliable means of safety interlock devices. 5418
Rationale: Clearance values specified in 5.4.2 are based on IEC 60664-1 and are specified 5419 for protection against electric shock. The values are the shortest distance 5420 through air between two different conductive parts. In that context, one conductor 5421 is at hazardous voltage (energy source) and another conductor is accessible to 5422 a person (body part). The required clearance is the minimum distance required 5423 to protect the person from being exposed to current causing electric shock. The 5424 distance acts as a safeguard against the hazardous energy source (ES2/ES3). 5425
– 156 – 108/757/DC
Contact gaps of interlock relays or switches are most likely not directly serving 5426 as the safeguard as explained above. Instead, the gap is meant to interrupt the 5427 electrical power to the energy sources, for example, motors generating MS2/3 5428 energy or laser units generating Class IIIb or larger energy. In this situation, the 5429 distance of the gap is required to interrupt the power supply to the device so 5430 that the device is shut down. Again, it is not for the purpose of blocking current 5431 to a body part. 5432
Although the purpose of the clearance is different, the required values based on 5433 IEC 60664-1 are used because there is no other data available addressing the 5434 minimum values required to establish circuit interruption to shut off the power to 5435 a load device. It is believed that the distance required to protect a person from 5436 shock hazard is sufficient to have a circuit interruption as part of proper circuit 5437 operation. The specified voltage in clause 5.4 is from 330 Vpeak or Vdc, and the 5438 contacts for interlock relays/switches most likely operate in DC low voltage such 5439 as 5 or 24 V, so much lower than 330 V. Mains operated contacts are required 5440 to have a gap for disconnect device that is much larger than the distance for 5441 insulation. 5442
Due to the above considerations, slight adjustment by altitude multiplication 5443 factor is not considered necessary for contact gaps of interlock relays/switches. 5444
___________ 5445
Annex L Disconnect devices 5446
Source: IEC 60065, IEC 60950-1 5447
Purpose: Primarily to provide a means to disconnect equipment from the mains for 5448 servicing, and secondarily to have available, if needed, a means to readily 5449 disconnect power for other reasons requiring power off. 5450
Rationale: Both IEC 60065 and IEC 60950 had a principle / requirement that a disconnect 5451 device was required for mains connected equipment for servicing. This also is 5452 the primary intent of the disconnect requirements in IEC 62368-1 although not 5453 stated in the Annex L requirement like it was in IEC 60065 and IEC 60950-1. 5454
For IEC 60950-1, since a significant portion of the equipment was permanently 5455 connected, or cord connected but large, sometimes with multiple cords (for 5456 example, in Data Centers), the need for a disconnect device for servicing was 5457 critical (via 3.4.2). When the purpose of the switch was not for servicing, like for 5458 paper shredders, another term was used like Isolating Switch (a form of a 5459 Disconnect Device), which is more aligned with the IEC defined term for 5460 “Isolation Device” (395-07-121), “a device in a circuit that prevents malfunction 5461 in one section of a circuit from causing unacceptable influences in other Sections 5462 of the circuit or other circuits.” 5463
IEC 60065 (via 5.5.3) also considered the need for a disconnect device to be 5464 readily operable (available) to turn off the equipment in case of an unexpected 5465 event, such as to prevent injury due to a defective safeguard, or for any other 5466 reason requiring power off. 5467
In IEC 62368-1, a disconnect device is used primarily as a means to disconnect 5468 power for servicing, whether permanent connected or cord-connected. 5469 Secondarily, it is available for use as means to disconnect power in an 5470 unexpected event or any other reason requiring power off. 5471
The technical requirements for disconnect devices in Annex L are based on the 5472 requirements for disconnect devices in both IEC 60065 (8.18) and IEC 60950-1 5473 (3.4.2). 5474
– 157 – 108/757/DC
For example, the 3 mm separation distance requirement has its origin with 5475 permanently connected equipment to provide additional assurance on integrity 5476 of the safeguard as skilled persons may be servicing circuits on the load side of 5477 the disconnect. Additionally, a clearance of 3 mm can withstand peak impulse 5478 voltages of 4 000 V, which corresponds to a transient overvoltage present in 5479 overvoltage category III environment (equipment as part of the building 5480 installation). 5481
___________ 5482
Annex M Equipment containing batteries and their protection circuits 5483
M.1 General requirements 5484
Rationale: Stand-alone battery chargers for general purpose batteries shall be evaluated 5485 using their relevant safety document, and not IEC 62368-1. If the battery and 5486 the charger are designed specifically for AV or ICT equipment and not to be used 5487 for other purposes, the provisions of IEC 62368-1, including Annex M may be 5488 applied. 5489
M.2 Safety of batteries and their cells 5490
Rationale: Equipment containing batteries shall be designed to reduce the risk of fire, 5491 explosion and chemical leaks under normal operating conditions and after a 5492 single fault condition in the equipment, including a fault in circuitry within the 5493 equipment battery pack. For batteries replaceable by an ordinary person or 5494 an instructed person, the design shall provide safeguards against reverse 5495 polarity installation or replacement of a battery pack from different component 5496 manufacturers if this would otherwise defeat a safeguard. 5497
Other clauses in this document address in generic terms safeguards associated 5498 with the use of batteries. This annex does not specifically address those 5499 safeguards, but it is expected that batteries and associated circuits conform to 5500 the relevant requirements in this document. 5501
This annex addresses safeguards that are unique to batteries and that are not 5502 addressed in other parts of the document. Energy sources that arise from the 5503 use of batteries are addressed in this annex and include the following: 5504
− situations where the battery is in a state that exceeds its specifications or 5505 ratings (for example, by overcharging, rapid-charge, rapid-discharge, 5506 overcurrent or overvoltage conditions); 5507
− thermal runaway due to overcharge or short circuits within battery cells; 5508
− reverse-charging of the battery; 5509
− leakage or spillage of electrolyte; 5510
− emission of explosive gases; and 5511
− location of safeguards where battery packs may be replaceable by an 5512 ordinary person or an instructed person. 5513
Thermal runaway in the cell can result in explosion or fire, when the 5514 temperature rise in the cell caused by the heat emission raises the internal cell 5515 pressure faster than can be released by the cell pressure release device. 5516 Thermal runaway can be initiated by several causes: 5517
− defects introduced into the cell during cell construction. These defects are 5518 often not detected during the manufacturing process and may bridge an 5519 internal insulation layer or block a vent; 5520
− over-charge and rapid-charge or rapid-discharge; 5521
− high operational temperature or high battery environment temperature; 5522
– 158 – 108/757/DC
− other cells in a pack feeding energy to a fault in a single cell; and 5523
− crushing of the enclosure. 5524
NOTE Batteries may contain multiple cells. 5525
During charging operation, gases are emitted from secondary cells and 5526 batteries excluding gastight sealed (secondary) cells, as the result of the 5527 electrolysis of water by electric current. Gases produced are hydrogen and 5528 oxygen. 5529
Table 18 in this document gives an overview of the referenced battery 5530 documents. 5531
5532
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Table 18 – Safety of batteries and their cells – requirements (expanded information on documents and scope) 5533
Document
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IEC 60086-4 (2014); Primary Batteries – Part 4 – Safety of Lithium Batteries
X X X Specifies tests and requirements for primary lithium batteries to ensure their safe operation under intended use and reasonably foreseeable misuse (including coin / button cell batteries).
IEC 60086-5 (2016): Primary Batteries – Part 5 – Safety of batteries with aqueous electrolyte
X X X Specifies tests and requirements for primary batteries with aqueous electrolyte to ensure their safe operation under intended use and reasonably foreseeable misuse (includes coin/button cell batteries).
IEC 60896-11 (2002): Stationary Lead Acid Batteries – Part 11 – Vented type
X X X X Applicable to lead-acid cells and batteries that are designed for service in fixed locations (for example, not habitually to be moved from place to place) and which are permanently connected to the load and to the DC power supply. Batteries operating in such applications are called "stationary batteries". Any type or construction of lead-acid battery may be used for stationary battery applications. Part 11 is applicable to vented types only.
IEC 60896-21 (2004): Stationary Lead Acid Batteries – Part 21 – Valve regulated type – method of test
X X X X Applies to all stationary lead-acid cells and monobloc batteries of the valve regulated type for float charge applications, (for example, permanently connected to a load and to a DC power supply), in a static location (for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to specify the methods of test for all types and construction of valve regulated stationary lead acid cells and monobloc batteries used in standby power applications.
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Document
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IEC 60896-22 (2004): Stationary Lead Acid Batteries – Part 22 – Valve regulated type – requirements
X X X X Applies to all stationary lead-acid cells and monobloc batteries of the valve regulated type for float charge applications, (for example, permanently connected to a load and to a DC power supply), in a static location (for example, not generally intended to be moved from place to place) and incorporated into stationary equipment or installed in battery rooms for use in telecom, uninterruptible power supply (UPS), utility switching, emergency power or similar applications. The objective is to assist the specifier in the understanding of the purpose of each test contained within IEC 60896-21 and provide guidance on a suitable requirement that will result in the battery meeting the needs of a particular industry application and operational condition. This document is used in conjunction with the common test methods described in IEC 60896-21 and is associated with all types and construction of valve regulated stationary lead-acid cells and monobloc batteries used in standby power applications.
IEC 61056-1 (2012): General purpose lead-acid batteries (valve-regulated types) – Part 1: General requirements, functional characteristics – Methods of test
X X X X Specifies the general requirements, functional characteristics and methods of test for all general-purpose lead-acid cells and batteries of the valve-regulated type:
– for either cyclic or float charge application;
– in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies.
(For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation).
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Document
Chemistry Category Movability
Scope (details)
Alk
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Lead
Aci
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Lith
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Nic
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alka
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Var
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IEC 61056-2 (2012): General purpose lead-acid batteries (valve-regulated types) – Part 2: Dimensions, terminals and marking
X X X X Specifies the dimensions, terminals and marking for all general-purpose lead-acid cells and batteries of the valve regulated type:
– for either cyclic or float charge application;
– in portable equipment, for instance, incorporated in tools, toys, or in static emergency, or uninterruptible power supply and general power supplies.
(For stationary applications, the battery will need to meet IEC 60896-21/-22 or subject to additional evaluation).
IEC 61427 (all parts) (2013): Secondary cells and batteries for renewable energy storage – General requirements and methods of test – Part 1: Photovoltaic off-grid application
X X X Part of a series that gives general information relating to the requirements for the secondary batteries used in photovoltaic energy systems (PVES) and to the typical methods of test used for the verification of battery performances. This part deals with cells and batteries used in photovoltaic off-grid applications. This document is applicable to all types of secondary batteries.
IEC TS 61430 (1997): Secondary Cells and Batteries – Test Methods for Checking the Performance of Devices Designed for Reducing Explosion Hazards – Lead-Acid Starter Batteries
X X X Specification gives guidance on procedures for testing the effectiveness of devices which are used to reduce the hazards of an explosion, together with the protective measures to be taken.
IEC 61434 (1996): Secondary cells and batteries containing alkaline or other non-acid electrolytes Guide to the designation of current in alkaline secondary cell and battery standards
X X X Applies to secondary cells and batteries containing alkaline or other non-acid electrolytes. It proposes a mathematically correct method of current designation which shall be used in future secondary cell and battery documents.
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Document
Chemistry Category Movability
Scope (details)
Alk
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IEC 61959 (2004): Secondary cells and batteries containing alkaline or other non-acid electrolytes Mechanical tests for sealed portable secondary cells and batteries
X X X Specifies tests and requirements for verifying the mechanical behavior of sealed portable secondary cells and batteries during handling and normal use.
IEC 62133 (all parts) (2012 – superseded by IEC 62133-1 and IEC 62133-2); Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications
X X X X* Specifies requirements and tests for the safe operation of portable sealed secondary cells and batteries (other than coin / button cell batteries) containing alkaline or other non-acid electrolyte, under intended use and reasonably foreseeable misuse.
IEC 62133-1 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary cells, and for batteries made from them, for use in portable applications – Part 1: Nickel systems
X X X Specifies requirements and tests for the safe operation of portable sealed secondary nickel cells and batteries containing alkaline electrolyte, under intended use and reasonably foreseeable misuse.
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Document
Chemistry Category Movability
Scope (details)
Alk
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IEC 62133-2 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for portable sealed secondary lithium cells, and for batteries made from them, for use in portable applications – Part 2: Lithium systems
X X X X* Specifies requirements and tests for the safe operation of portable sealed secondary lithium cells and batteries containing non-acid electrolyte, under intended use and reasonably foreseeable misuse.
IEC 62281 (2016): Safety of primary and secondary lithium cells and batteries during transport
X X X X Specifies test methods and requirements for primary and secondary (rechargeable) lithium cells and batteries to ensure their safety during transport other than for recycling or disposal (similar to UN 38.3).
IEC 62485-2
(2010): Safety requirements for secondary batteries and battery installations – Part 2: Stationary batteries
X X X X Applies to stationary secondary batteries and battery installations with a maximum voltage of 1 500 V DC (nominal) and describes the principal measures for protections against hazards generated from:
– electricity,
– gas emission,
– electrolyte.
Provides requirements on safety aspects associated with the erection, use, inspection, maintenance and disposal. It covers lead-acid and NiCd/NiMH batteries (IEC 62485-2 requires the valve regulated batteries to meet safety requirements from IEC 60896).
– 164 – 108/757/DC
Document
Chemistry Category Movability
Scope (details)
Alk
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Aci
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IEC 62619 (2017): Secondary cells and batteries containing alkaline or other non-acid electrolytes – Safety requirements for secondary lithium cells and batteries, for use in industrial applications
X X X Specifies requirements and tests for the safe operation of secondary lithium cells and batteries used in industrial applications including stationary applications.
* IEC 62133-2 (2017) may be used with stationary equipment for sub-system powering. Such batteries/packs typically are a similar format as batteries and battery packs used in portable equipment and only provide sub-system powering of part(s) of the equipment for orderly shutdown and similar functional purposes in the event of power loss (compared to storage batteries for full system powering).
5534
– 165 – 108/757/DC
M.3 Protection circuits for batteries provided within the equipment 5535
Rationale: Equipment containing batteries is categorized into two types; 5536
1. Equipment containing batteries which are embedded in the equipment and 5537 cannot be separated from the equipment. 5538
2. Equipment containing batteries which can be separated from the equipment. 5539
The requirements in IEC 62368-1 cover only the battery circuits that are not an 5540 integral part of the battery itself, and as such form a part of the equipment. 5541
M.4 Additional safeguards for equipment containing a portable secondary lithium 5542 battery 5543
Rationale: M.4 applies to all equipment with lithium batteries. M.4.4 applies only to 5544 equipment as specified in M.4.4 (typically portable equipment). 5545
Secondary lithium batteries (often called lithium-ion or li-ion batteries) are 5546 expected to have high performance, such as light-weight and high energy 5547 capability. The use of li-ion batteries has been continuously expanding in the 5548 area of high-tech electronic equipment. However, it is said that this technology 5549 involves risks because the safety margin (distance between safe-operation zone 5550 and unsafe-operation zone) is relatively small compared to other battery 5551 technologies. 5552
IEC TC 108 noted that for designing equipment containing or using li-ion battery, 5553 it is imperative to give careful consideration to selecting highly reliable battery 5554 cells, providing high performance battery management systems for operating 5555 batteries within their specified operating environment and parameter range (for 5556 example, battery surrounding temperature or battery charging/discharging 5557 voltage and current). It is also imperative to introduce safeguards against 5558 abnormal operating conditions, such as vibration during the use of devices, 5559 mechanical shock due to equipment drop, surge signals caused internally or 5560 externally, and a mechanism to reduce the likelihood of catastrophic failure such 5561 as battery explosion or fire. 5562
It is suggested that suppliers of equipment and batteries should take into 5563 account possible abnormal operating conditions that may occur during use, 5564 transport, stock, and disposal, so that the equipment is well prepared for such 5565 conditions. 5566
It is important that the key parameters (highest/lowest charging temperatures, 5567 maximum charging current, and upper limit charging voltage) during charging 5568 and discharging of the battery are not exceeded. 5569
IEC TC 108 noted that, when designing battery compartments, the battery 5570 compartment dimensions should allow sufficient space for cells to expand 5571 normally under full operating temperature range or be flexible to prevent 5572 unnecessary compression of the cells. Given the wide range of battery 5573 constructions, corresponding battery compartment dimensional requirements 5574 will differ. When necessary, coordinate with the battery manufacturer to 5575 determine change in battery dimensions over full operating range during 5576 charging and discharging. 5577
M.4.1 General 5578
Rationale: Sub-clause M.2.1 contains a list of IEC standard for batteries that are normative 5579 for batteries and cells that are relevant based on their intended use. Included in 5580 the list is IEC 62619, which mentions in its scope, “… specifies requirements and 5581 tests for the safe operation of secondary lithium cells and batteries used in 5582 industrial applications including stationary applications.” “Telecommunication” 5583 equipment is one of the stationary equipment applications given as an example 5584 under its scope. 5585
5586
– 166 – 108/757/DC
Included in IEC 62619 in Clause 8 are requirements for battery system safety 5587 (considering functional safety, Clause 8.1), which also includes specific 5588 requirements for the battery management system, BMS (8.2.1). While the BMS 5589 requirements in 8.2.1 are relatively similar in nature to IEC 62133-2 and Annex M 5590 of IEC 62368-1, the provision for additional investigation of electric, electronic 5591 and software controls and systems used for critical safety is not something 5592 covered by IEC 62133-2 and Annex M to the degree as it is covered in 5593 IEC 62619. 5594
Therefore, if batteries (including battery packs) intended for transportable 5595 equipment are used in stationary equipment it is appropriate to consider the 5596 requirements of 8.1 of IEC 62619 if electric, electronic and software controls and 5597 systems are relied upon as the primary safeguard for safety of the battery, 5598 provided the battery is not provided with a supplementary safeguard. 5599
M.4.2.2 Compliance criteria 5600
The highest temperature point in the battery may not always exist at the center 5601 of the battery. The battery supplier should specify the point where the highest 5602 temperature in the battery occurs. 5603
To test the charging circuit, instead of using a real battery (which is a chemical 5604 system), an electrical circuit emulating the battery behavior (dummy battery 5605 circuit) may make the test easier by eliminating a possible battery defect. 5606
An example of a dummy battery circuit is given in Figure 58 in this document. 5607
Figure 58 – Example of a dummy battery circuit
M.4.3 Fire enclosure 5608
Lithium-ion batteries with an energy more than PS1 (15 W) must be provided 5609 with a fire enclosure (either at the battery or at the equipment containing the 5610 battery) because even though measurements of output voltage and current may 5611 not necessarily show them to be a PIS, however they contain flammable 5612 electrolyte that can be easily ignited by the enormous amount of heat developed 5613 by internal shorts as a result of possible contaminants in the electrolyte. 5614
M.4.4 Drop test of equipment containing a secondary lithium battery 5615
Annex M.4.4 applies only to batteries used in portable applications. 5616
This includes batteries in the scope of IEC 62133 and IEC 62133-2 which are 5617 typically used in hand-held equipment or transportable equipment. 5618
Batteries or sub-assemblies containing batteries used in other types of 5619 equipment, that are not routinely held or carried but may be occasionally 5620 removed for service or replacement, are not considered to be portable batteries 5621 and are not in scope of Annex M.4.4. 5622
– 167 – 108/757/DC
Monitoring of lithium-ion battery output voltage and surface temperature during 5623 or after the drop test may not help. The concern is that if a minor dent occurs, 5624 nothing may happen to the battery. Temperature may go up slightly and then 5625 drop down without any significant failure. If the battery is damaged, the damage 5626 may only show up if the battery is then subjected to few charging and 5627 discharging cycles. Therefore, the surface temperature measurement was 5628 deleted and replaced with charging and discharging cycles after the drop test. 5629 The charging and discharging of the battery shall not result in any fire or 5630 explosion. 5631
It is important that the equipment containing a secondary lithium battery 5632 needs to have a drop impact resistance. Equipment containing a secondary 5633 lithium battery should avoid further damage to the control circuit and the 5634 batteries. 5635
As M.4.4 requires the equipment to be tested, the relevant equipment heights 5636 need to be used instead of the height for testing parts that act as a fire 5637 enclosure. 5638
After the drop test: 5639
− Initially, the control functions should be checked to determine if they continue 5640 to operate and all safeguards are effective. A dummy battery or appropriate 5641 measurement tool can be used for checking the function of the equipment. 5642
− Then, the batteries are checked whether or not a slight internal short circuit 5643 occurs. 5644
Discharge and charge cycles under normal operating conditions test hinder 5645 detection of the slight internal short circuit because the current to discharge and 5646 charge is higher than the current caused by a slight internal short circuit. 5647
Thus, it is very important to conduct a voltage observation of the battery 5648 immediately after the drop test without any discharge and charge. 5649
To detect a slight internal short circuit of the battery, IEC TC 108 adopts a no-5650 load test, which can detect a battery open voltage drop caused by an internal 5651 short circuit leak current in a 24 h period. 5652
Equipment containing an embedded type of battery has internal power 5653 dissipation (internal consumption current). Therefore, two samples of the 5654 equipment are prepared, one for the drop test and the other for reference in a 5655 standby mode. In this way, the effect of internal power dissipation can be 5656 detected by measuring a difference between voltage drops in the 24 h period. 5657
M.6.1 Requirements 5658
Examples: Examples of battery documents containing an internal short test are IEC 62133, 5659 IEC 62133-2 and IEC 62619. 5660
Another example of compliance to internal fault requirements is a battery using 5661 cells that have passed the impact test as specified in IEC 62281. 5662
M.7.1 Ventilation preventing an explosive gas concentration 5663
Rationale: During charging, float charging, and overcharging operation, gases are emitted 5664 from secondary cells and batteries excluding gastight sealed (secondary) cells, 5665 as the result of the electrolysis of water by electric current. Gases produced are 5666 hydrogen and oxygen. 5667
M.7.2 Test method and compliance criteria 5668
Source: The formula comes from IEC 62485-2:2010, 7.2. 5669
M.8.2.1 General 5670
Source: The formula comes from IEC 60079-10-1:2015, Clause B.4. 5671
___________ 5672
– 168 – 108/757/DC
Annex O Measurement of creepage distances and clearances 5673
Source: IEC 60664-1, IEC 60950-1 5674
Purpose: Clearances are measured from the X-points in the figure 5675
Rationale: Figure O.4. At an IEC/TC 109 meeting in Paris, a draft CTL interpretation was 5676 discussed regarding example 11 of IEC 60664-1:2007. The question was if 5677 distances smaller than X should be counted as zero. There was a quite lengthy 5678 debate, but the conclusion was that, based on the other examples in the standard 5679 (and especially example 1), there is no reason why in this example the distance 5680 should be counted as zero. If this should be done, many other examples should 5681 be changed where it is shown that the distance is measured across X rather than 5682 to disregard X. TC 109 has decided to modify the example 11 to remove the X 5683 from the figure to avoid this confusion in future. This is now represented in 5684 Figure 14 of IEC 60664-1:2020. As a result, the statement that distances smaller 5685 than X are disregarded is deleted from Figure O.4. 5686
Figure O.13. The clearance determination is made from the X-points in the 5687 figure, as those are the first contact points when the test finger enters the 5688 enclosure opening. It is assumed that the enclosure is covered by conductive 5689 foil, which simulates conductive pollution. 5690
___________ 5691
Annex P Safeguards against conductive objects 5692
P.1 General 5693
Rationale: The basic safeguard against entry of a foreign object is that persons are not 5694 expected to insert a foreign object into the equipment. Where the equipment is 5695 used in locations where children may be present, it is expected that there will be 5696 adult supervision to address the issue of reasonably foreseeable misuse by 5697 children, such as inserting foreign objects. Therefore, the safeguards specified 5698 in this annex are supplementary safeguards. 5699
P.2 Safeguards against entry or consequences of entry of a foreign object 5700
Source: IEC 60950-1 5701
Purpose: Protect against the entry of foreign objects 5702
Rationale: There are two alternative methods that may be used. 5703
P.2.2 specifies maximum size limits and construction of openings. The relatively 5704 small foreign conductive objects or amounts of liquids that may pass through 5705 these openings are not likely to defeat any equipment safeguards. This option 5706 prevents entry of objects that may defeat a safeguard. 5707
Alternatively, if the openings are larger than those specified in P.2.2, P.2.3 5708 assumes that a foreign conductive object or liquid passing through these 5709 openings is likely to defeat an equipment basic safeguard, and requires that the 5710 foreign conductive object or liquid shall not defeat an equipment supplementary 5711 safeguard or an equipment reinforced safeguard. 5712
P.2.3.1 Safeguard requirements 5713
Rationale: Conformal coating material is applied to electronic circuitry to act as protection 5714 against moisture, dust, chemicals, and temperature extremes that, if uncoated 5715 (non-protected), could result in damage or failure of the electronics to function. 5716 When electronics are subject to harsh environments and added protection is 5717 necessary, most circuit board assembly houses coat assemblies with a layer of 5718 transparent conformal coating rather than potting. 5719
– 169 – 108/757/DC
The coating material can be applied by various methods, from brushing, spraying 5720 and dipping, or, due to the increasing complexities of the electronic boards being 5721 designed and with the 'process window' becoming smaller and smaller, by 5722 selectively coating via robot. 5723
P.3 Safeguards against spillage of internal liquids 5724
Source: IEC 60950-1 5725
Rationale: If the liquid is conductive, flammable, toxic, or corrosive, then the liquid shall not 5726 be accessible if it spills out. The container of the liquid provides a basic 5727 safeguard. After the liquid spills out, then barrier, guard or enclosure that 5728 prevents access to the liquid acts as a supplementary safeguard. Another 5729 choice is to provide a container that does not leak or permit spillage for example, 5730 provide a reinforced safeguard. 5731
P.4 Metalized coatings and adhesives securing parts 5732
Source: IEC 60950-1 5733
Rationale: Equipment having internal barriers secured by adhesive are subject to 5734 mechanical tests after an aging test. If the barrier does not dislodge as a whole 5735 or partially or fall off, securement by adhesive is considered acceptable. 5736
The temperature for conditioning should be based on the actual temperature of 5737 the adhesive secured part. 5738
The test program for metalized coatings is the same as for aging of adhesives. 5739 In addition, the abrasion resistance test is done to see if particles fall off from 5740 the metalized coating. Alternatively, clearance and creepage distances for PD3 5741 shall be provided. 5742
___________ 5743
Annex Q Circuits intended for interconnection with building wiring 5744
Source: IEC 60950-1:2013 5745
Rationale: For the countries that have electrical and fire codes based on NFPA 70, this 5746 annex is applied to ports or circuits for external circuits that are interconnected 5747 to building wiring for limited power circuits. Annex Q was based on requirements 5748 from IEC 60950-1 that are designed to comply with the external circuit power 5749 source requirements necessary for compliance with the electrical codes noted 5750 above. 5751
Q.1.1 Requirements 5752
Rationale: Tables Q.1 and Q.2 have their origins through association with “Class 2” circuit 5753 requirements in NFPA 70, National Electrical Code (NEC). As 60 Vdc is inherent 5754 to the Class 2 definition, to maintain consistency and allow for adequate 5755 safeguarding of building wiring, any device, including IC Current Limiters, used 5756 to supply a Limited Power Source is required to have similar characteristics, 5757 including the 60 Vdc voltage limitation. Current Limiters used for purposes other 5758 than LPS do not have such a voltage limitation, although other Clauses, such as 5759 Clause 5, may place additional restrictions on their ratings and acceptable use. 5760
Q.1.2 Test method and compliance criteria 5761
In determining if a circuit is a limited power source, all conditions of use should 5762 be considered. For example, for circuits that may be connected to a battery 5763 source as well as a mains source, determination whether the available output 5764 from the circuit is a limited power source is made with each of the sources 5765 connected independently or simultaneously (see Figure 59 in this document). 5766
– 170 – 108/757/DC Q.2 Test for external circuits – paired conductor cable 5767
Time/current characteristics of type gD and type gN fuses specified in 5768 IEC 60269-2-1 comply with the limit. Type gD or type gN fuses rated 1 A, would 5769 meet the 1,3 A current limit. 5770
5771
Figure 59 – Example of a circuit with two power sources 5772
___________ 5773
Annex R Limited short-circuit test 5774
Source: IEC SC22E 5775
Rationale: The value of 1 500 A is aligned with the normal breaking capacity of a high 5776 breaking fuse. In Japan the prospective short circuit current is considered less 5777 than 1 000 A. 5778
___________ 5779
Annex S Tests for resistance to heat and fire 5780
S.1 Flammability test for fire enclosure and fire barrier materials of equipment where 5781 the steady-state power does not exceed 4 000 W 5782
Rationale: This test is intended to test the ability of an end-product enclosure to adequately 5783 limit the spread of flame from a potential ignition source to the outside of the 5784 product. 5785
− Included the text from IEC 60065 using the needle flame as the ignition source 5786 for all material testing. The reapplication of the flame after the first flaming 5787 was added to clarify that the test flame is immediately re-applied based on 5788 current practices. 5789
− This conditioning requirement of 125 °C for printed wiring boards is derived 5790 from laminate and PCB documents. 5791
S.2 Flammability test for fire enclosure and fire barrier integrity 5792
Rationale: This test method is used to test the integrity of a fire barrier or fire enclosure 5793 where a potential ignition source is in very close proximity to an enclosure or 5794 a barrier. 5795
The criteria of “no additional holes” is considered important as flammable 5796 materials may be located immediately on the other side of the barrier or fire 5797 enclosure. 5798
Rationale: Application of needle flame 5799
– 171 – 108/757/DC
The flame cone and the 50 mm distance is a new requirement that was not 5800 applied in IEC 60950 to top openings. This new requirement does impact already 5801 certified IEC 60950 ITE products, and it was found that some manufacturers’ 5802 current designs were not able to comply with the 50-mm distance prescribed 5803 ventilation opening requirements and will not be able to pass the needle flame 5804 test as per IEC 60695-11. An HBSDT’s fire enclosure adhoc team performed 5805 some experimental flame testing with the needle flame located at various 5806 distances from various size ventilation openings. This test approach was found 5807 to align more with hazard-based safety engineering principles and deemed to be 5808 a more realistic representation of when a thermal event may occur. 5809
A PIS can be in the form of any size/shape, so it was determined not reasonable 5810 to directly apply the needle flame to top surface openings when realistically a 5811 thermal event from smaller components is unlikely to touch the top surface 5812 openings. Additionally, typically it is common for such components to be 5813 mounted on V-0 rated boards that further help reduce the spread of fire. 5814
The test data from the fire experimental testing demonstrated clearly that, when 5815 the flame is at distances well within 50 mm, significantly larger openings can be 5816 used beyond the pre-specified sizes by 6.4.8.3.3 (for example less than 5 mm in 5817 any dimension and/or less than 1 mm regardless of length). 5818
Therefore, for the purpose of this standard and to align more with hazard-based 5819 safety engineering principles, the needle flame is to be applied at a distance 5820 measured from the closest assessed point of a PIS to the closest surface point 5821 of the test specimen. The application of the flame is measured from the top of 5822 the needle flame burner to the closest surface point. See Figure S.1 in Clause 5823 S.2. 5824
S.3 Flammability tests for the bottom of a fire enclosure 5825
Source: IEC 60950-1:2013 5826
Rationale: This text was not changed from the original ECMA document which was originally 5827 in IEC 60950-1. This test is intended to determine the acceptability of holes or 5828 hole patterns in bottom enclosures to prevent flaming material from falling onto 5829 the supporting surface. It has been used principally for testing metal bottom 5830 enclosures. 5831
This test is being proposed to test all bottom enclosures. Research is ongoing 5832 to develop a similar test based on the use of flammable (molten) thermoplastic 5833 rather than oil. 5834
S.4 Flammability classification of materials 5835
Rationale: The tables were considered helpful to explain the hierarchy of material 5836 flammability class requirements used in this document. 5837
Whenever a certain flammability class is required, a better classification is 5838 allowed to be used. 5839
S.5 Flammability test for fire enclosure materials of equipment with a steady state 5840 power exceeding 4 000 W 5841
Source: IEC 60950-1:2013 5842
Rationale: The annex for flammability test for high voltage cables was withdrawn and 5843 replaced by flammability test for fire enclosure materials of equipment having 5844 greater than 4 000 W faults. 5845
___________ 5846
– 172 – 108/757/DC
Annex T Mechanical strength tests 5847
T.2 Steady force test, 10 N 5848
Source: IEC 60950-1 5849
Rationale: 10 N applied to components and parts that may be touched during operation or 5850 servicing. This test simulates the accidental contact with a finger or part of a 5851 hand. 5852
T.3 Steady force test, 30 N 5853
Source: IEC 60065 and IEC 60950-1 5854
Rationale: This test simulates accidental contact with a part of the hand. 5855
T.4 Steady force test, 100 N 5856
Source: IEC 60065 and IEC 60950-1 5857
Rationale: This test simulates an expected force applied during use or movement. 5858
T.5 Steady force test, 250 N 5859
Source: IEC 60065 and IEC 60950-1 5860
Rationale: 250 N applied to external enclosures (except those covered in Clause T.4). This 5861 test simulates an expected force when leaning against the equipment surface to 5862 ensure clearances are not bridged to introduce a hazard such as shock. The 5863 30 mm diameter surface simulates a small part of hand or foot. It is not expected 5864 that such forces will be applied to the bottom surface of heavy equipment 5865 (> 18 kg). 5866
T.6 Enclosure impact test 5867
Source: IEC 60065 and IEC 60950-1 5868
Rationale: To check integrity of the enclosure, to ensure that no hazard is created by an 5869 impact. 5870
The values in T.6 are taken over from existing requirements in IEC 60065 and 5871 IEC 60950-1. 5872
The impact is applied once for each test point on the enclosure. 5873
T.7 Drop test 5874
Source: IEC 60065 and IEC 60950-1 5875
Rationale: This test addresses potential exposure to a hazard after the impact and not 5876 impact directly on a body part. The test is applied to desk top equipment under 5877 7 kg as it is more likely these products could be accidentally knocked off the 5878 desk. The drop height was chosen based on intended use of the product. 5879
The term “table-top” has been used in IEC 60065, while the term “desk-top” has 5880 been used in IEC 60950-1. Both terms had been taken over in IEC 62368-1 5881 without the intention to make the different requirements for these types of 5882 equipment. Therefore, the requirements are applicable to both type of equipment 5883 even if only either one is referred to. From edition 3 onwards, the term “table-5884 top” has been replaced by “desk-top”. 5885
T.8 Stress relief test 5886
Source: IEC 60065 and IEC 60950-1 5887
Rationale: To ensure that the mechanical integrity of moulded plastic parts is not affected 5888 by their relaxation or warping following thermal stress. 5889
T.9 Glass impact test 5890
Source: IEC 60065 5891
– 173 – 108/757/DC Rationale: Test applied to test the strength of the glass. 5892
The value of 7 J is a value that has been used for CRT in the past. Except for 5893 that, the value has also been used in commercial applications, but not in 5894 households, where the forces expected on the glass are much lower. CRT’s have 5895 separate requirements in Annex W. Therefore, a value of 3,5 J is considered 5896 sufficient. 5897
The centre of a piece of glass can be determined via the intersection of two 5898 diagonals for a rectangular piece or any other appropriate means for pieces of 5899 other geometries. 5900
T.10 Glass fragmentation test 5901
Source: IEC 60065 5902
Rationale: Test applied to ensure the fragments are small enough to be considered at MS2 5903 level or less. 5904
___________ 5905
Annex U Mechanical strength of CRTs and protection against the effects of 5906 implosion 5907
U.2 Test method and compliance criteria for non-intrinsically protected CRTs 5908
Source: IEC 61965, IEC 60065 5909
Rationale: The 750 mm simulates the height of a typical supporting surface such as a table 5910 or counter top. Test applied to ensure any expelled fragments are small enough 5911 to be considered at MS2 level or less. The fragment size represents a grain of 5912 sand. The test distances selected ensure fragments do not travel far enough to 5913 strike a person and cause injury. 5914
___________ 5915
Annex V Determination of accessible parts 5916
Figure V.3 Blunt probe 5917
Source: This test probe is taken from Figure 2c, IEC 60950-1:2013 5918
___________ 5919
Annex X Alternative method for determining clearances for insulation in 5920 circuits connected to an AC mains not exceeding 420 V peak (300 V 5921 RMS) 5922
Rationale: IEC TC 108 made a responsible decision to harmonize the requirements for 5923 clearances and creepage distances with the horizontal IEC 60664-x series 5924 documents produced by IEC TC 109. This decision is aligned with IEC 5925 harmonization directives and allows manufacturers the design benefits afforded 5926 by the IEC 60664-x series documents when minimization of spacings is a primary 5927 consideration of the product design. 5928
– 174 – 108/757/DC
However, because of the complexity of determining clearances as per 5.4.2, 5929 sometimes the more state-of-art theory is not practical to implement for designs 5930 not requiring minimized spacings. For example, there are a very large number of 5931 existing designs and constructions qualified to IEC 60950-1 that are associated 5932 with products, mainly switch mode power supplies, connected to AC mains 5933 (overvoltage category II) not exceeding 300 V RMS. These constructions have 5934 successfully used the clearance requirements in IEC 60950-1 without any 5935 evidence of field issues, and even at switching frequencies well above 30 kHz. 5936 In fact, almost every switch mode power supply (SMPS) used today with IT & 5937 ICT equipment intended to be connected to mains less than 300 V RMS, 5938 including external power supplies, direct plug-in type, and internal power 5939 supplies, have clearances based on the base requirements in Subclause 5940 2.10.3.3 and Tables 2K and 2L of IEC 60950-1. Although the requirements do 5941 not incorporate the latest research on clearances used in circuits operating 5942 above 30 kHz, they are considered to be suitable for the application because 5943 they are a conservative implementation of IEC 60664-1 without minimization. 5944
As a result, and in particular based on their proven history of acceptability in the 5945 broad variety of power supplies used today, IEC TC 108 should support 5946 continued limited application of a prescribed set of clearances as an alternative 5947 to the more state-of-art IEC 60664-based requirements in IEC 62368-1 today. 5948 However, because of the valid concern with circuits operating above 30 kHz as 5949 clearances are further minimized, the IEC 60950-1 option in Tables 2K and 2L 5950 for reduced clearances in products with manufacturing subjected to a quality 5951 control programme (values in parenthesis in Tables 2K/2L) are not included in 5952 this proposal since the reduced clearances associated with the quality control 5953 option has not been used frequently under IEC 60950-1, and therefore there is 5954 not the same proven track record of successful implementation in a very large 5955 number of products. Similarly, there is not the same large quantity of qualified 5956 designs/construction associated with equipment connected to mains voltages 5957 exceeding 300 V RMS, or for equipment connected to DC mains, so these 5958 constructions should comply with the existing IEC 60664-based requirements in 5959 IEC 62368-1. 5960
___________ 5961
Annex Y Construction requirements for outdoor enclosures 5962
Rationale: General 5963
In preparing the requirements for outdoor enclosures, it has been assumed 5964 that: 5965
– exterior to the outdoor equipment there should be no hazards, just as is the 5966 case with other information technology equipment; 5967
– protection against vandalism and other purposeful acts will be treated as a 5968 product quality issue (for example, IEC 62368-1 does not contain 5969 requirements for the security of locks, types of acceptable screw head, forced 5970 entry tests, etc.). 5971
Electric shock 5972
It is believed that most aspects relating to protection against the risk of electric 5973 shock are adequately covered by IEC 62368-1 including current proposals, and 5974 in some cases, quoted safety documents (in particular, the IEC 60364 series), 5975 and with the exception of the following, do not require modification. Specific 5976 requirements not already suitably addressed in IEC 60950-1 were considered as 5977 follows: 5978
– clearing of earth faults for remotely located (exposed) information technology 5979 equipment; 5980
– the degree of protection provided by the enclosure to rain, dust, etc.; 5981
– 175 – 108/757/DC
– the effect of moisture and pollution degree on the insulation of the enclosed 5982 parts; 5983
– the possible consequences of ingress by plants and animals (since these 5984 could bridge or damage insulation); 5985
– the maximum permissible touch voltage and body contact impedance for wet 5986 conditions. 5987
It is noted that the voltage limits of user-accessible circuits and parts in outdoor 5988 locations only are applicable to circuits and parts that are actually “user-5989 accessible”. If the circuits and parts are not user accessible (determined via 5990 application of accessibility probes) and are enclosed in electrical enclosures, 5991 connectors and cable suitable for the outdoor application, including being subject 5992 to all relevant outdoor enclosure testing, voltage limits for indoor locations may 5993 be acceptable based on the application. For example, a power-over-ethernet 5994 (PoE) surveillance camera mounted outdoors supplied by 48 V DC from PoE 5995 would be in compliance with Clause 5 if the electrical enclosure met the 5996 applicable requirements for outdoor enclosures. 5997
Fire 5998
It is believed that most aspects relating to protection against fire emanating from 5999 within the equipment are adequately covered by IEC 62368-1. However, certain 6000 measures that may be acceptable for equipment located inside a building would 6001 not be acceptable outdoors because they would permit the entry of rain, etc. 6002
For certain types of outdoor equipment, it could be appropriate to allow the ‘no 6003 bottom fire enclosure required if mounted on a concrete base’ exemption that 6004 presently can be used for equipment for use within a restricted access location. 6005
Mechanical hazards 6006
It is believed that all aspects relating to protection against mechanical hazards 6007 emanating from the equipment are adequately covered by IEC 62368-1. 6008
Heat-related hazards 6009
It is believed that most aspects relating to protection against direct heat hazards 6010 are adequately covered by IEC 62368-1. However, it may be appropriate to 6011 permit higher limits for equipment that is unlikely to be touched by passersby (for 6012 example, equipment that is only intended to be pole mounted out of reach). A 6013 default nominal ambient temperature range for outdoor equipment has been 6014 proposed. The effects of solar heating have not been addressed. 6015
In addition to direct thermal hazards, there is a need to consider consequential 6016 hazards. For instance, some plastics become brittle as they become cold. An 6017 enclosure made from such brittle plastic could expose users to other hazards 6018 (for example, electrical or mechanical) if it were to break. 6019
Radiation 6020
It is believed that most aspects relating to direct protection against radiation 6021 hazards are adequately covered by IEC 62368-1. However, there may be 6022 consequential hazards to consider. Just as polymeric materials can be affected 6023 by low temperatures, they can also become embrittled owing to the effect of UV 6024 radiation. An enclosure made from such brittle plastic could expose users to 6025 other hazards (for example, electrical or mechanical) if it were to break. 6026
Chemical hazards 6027
It is believed that certain types of outdoor equipment need to have measures 6028 relating to chemical hazards originating within, or external to, the equipment. 6029 Exposure to chemicals in the environment (for example, salt used to clear roads 6030 in the winter) can also cause problems. 6031
– 176 – 108/757/DC
Biological hazards 6032
These are not presently addressed in IEC 62368-1. As with radiation hazards 6033 and chemical hazards, it is thought that there is not likely to be any direct 6034 biological hazard. However, plastics and some metals can be attacked by fungi 6035 or bacteria and this could result in weakening of protective enclosures. As 6036 stated under 'electric shock', the ingress of plants and animals could result in 6037 damage to insulation. 6038
Explosion hazards 6039
Outdoor equipment may need to be weather-tight, in such cases there is an 6040 increased probability that an explosive atmosphere can build up as a result of: 6041
– hydrogen being produced as a result of charging lead-acid batteries within 6042 the equipment and; 6043
– methane and other ‘duct gasses’ entering the equipment from the outdoors. 6044
Y.3 Resistance to corrosion 6045
Rationale: Enclosures made of the following materials are considered to comply with XX.1 6046 without test: 6047
(a) Copper, aluminum, or stainless steel; and 6048
(b) Bronze or brass containing at least 80 % copper. 6049
Y.4.6 Securing means 6050
Rationale: Gaskets associated with doors, panels or similar parts subject to periodic 6051 opening is an example of a gasket needing either mechanical securement or 6052 adhesive testing. 6053
___________ 6054
6055
– 177 – 108/757/DC
Annex A 6056
(informative) 6057
6058
Background information related to the use of surge suppressors 6059
NOTE The content of this Annex is provided for information only. This Annex does not in any way override the 6060 requirements in IEC standards, nor does it provide examples of universally accepted constructions. 6061
A.1 Industry demand for incorporating surge suppressors in the equipment 6062
The industry has the demand of providing protection of communication equipment from 6063 overvoltage that may be caused by lightning strike surge effect. There are reports in Japan that 6064 hundreds of products are damaged by lightening surges every year, including the risk of fire 6065 and/or electrical shock according to the damage to the equipment, especially in the regions 6066 where many thunderstorms are observed. We believe it will be the same in many other countries 6067 by the reason described in the next paragraph where the voltage of the surge is much higher 6068 than expected value for overvoltage category II equipment (1 500 V peak or 2 500 V peak). For 6069 the surge protection purpose, the manufacturers have need to introduce the surge protection 6070 devices in the equipment, not only for class I equipment but also for class II equipment or 6071 class III equipment, but facing to the difficulty of designing equipment because of the limited 6072 acceptance in IEC 62368-1. 6073
If the point of bonding for mains to the equipment is not adjacent to the point of bonding of 6074 telecommunication line that is connected to the external circuit of the same equipment, the 6075 surge entered from the power line or from the telecommunication line causes the high potential 6076 difference on the insulation in the equipment, and causes the insulation/component breakdown 6077 which may cause product unuseable. 6078
In some cases, the damage on the insulation or safeguard can cause hazardous voltage on 6079 ES1 or an accessible metal part, or an insulation material heating up or catching fire (see 6080 Figure A.1 in this document, with the example of class II equipment.) 6081
The most effective way to protect equipment from a lightning surge is, as commonly understood 6082 internationally, to have an equipotential bonding system in the building/facility with a very low 6083 in-circuit impedance by the use of main-earth bar concept (see Figure A.2 in this document). 6084 This kind of high-quality earthing provision can be introduced in the building/facility in the 6085 business area, such as computer rooms, or in modern buildings. 6086
This kind of high quality earthing provision may not always be possible in the residential area, 6087 in already-existing buildings and in some countries where the reliable low impedance earth 6088 connection may not be easily obtained from technical (according to the characteristics of land) 6089 or even by practical reasons (because very expensive construction change to the building is 6090 required, or according to the lack of regulatory co-work it is difficult to get the relevant 6091 permission for cabling). We should not disregard the fact that many ICT equipment (including 6092 PCs, fax machines, TVs and printers) are brought to home, school and small business offices 6093 in the existing buildings (see Figure A.3 in this document). 6094
If the use of surge suppressors configured by an MOV, such as a varistor in series with a GDT, 6095 is allowed in the equipment to bridge safeguards, it is effective to avoid the possibility that the 6096 lightening surge breaks the circuit or the insulation within the equipment (see Figure A.4 in this 6097 document). 6098
Thus, there is industry demand for using surge protecting devices (SPDs) in the equipment 6099 independent of whether the product is class I equipment, class II equipment or class III 6100 equipment. 6101
– 178 – 108/757/DC
6102
Figure A.1 – Installation has poor earthing and bonding; 6103 equipment damaged (from ITU-T K.66) 6104
6105
Figure A.2 – Installation has poor earthing and bonding; using main earth bar 6106 for protection against lightning strike (from ITU-T K.66) 6107
6108
– 179 – 108/757/DC
6109
Figure A.3 – Installation with poor earthing and bonding, using a varistor 6110
6111
Figure A.4 – Typîcal example of a surge suppressor and a voltage fall 6112
– 6113
A.2 Considerations on surge suppressors bridging both sides of a safeguard 6114
For a surge suppressor that bridges both sides of the insulation safeguard, the followings need 6115 to be considered in order to prevent hazards due to the bridging. 6116
The surge suppressor with a group of SPCs bridging between the mains and an external circuit 6117 shall not operate during a single fault condition at the power distribution system or in a surge 6118 suppressor to make sure that any hazardous voltage shall not appear at an accessible part of 6119 the equipment. 6120
Following situations shall not create a leak to the ES1 and ES2 circuits: 6121
– follow-on current triggered by a surge voltage (caused by lightning and power system 6122 switching); 6123
– temporary overvoltage (TOV) caused by a failure in the power distribution system, and 6124
– fluctuation of the mains voltage. 6125
– 180 – 108/757/DC Surge voltages on an external circuit cable do not cause a hazard and it are allowed to appear 6126 on an external circuit. (see 5.4.2.3.2.4 of IEC 62368-1:2021). 6127
It is commonly known that surge voltages often appear on external circuit of ID1 in Table 13 of 6128 IEC 62368-1. Also, the surge voltages do not change even if a surge suppressor bridges the 6129 mains and the external circuit operates. 6130
The follow-on current does not appear if a surge suppressor is configured by a series 6131 combination of a GDT and a varistor. In this case, the varistor shall have an operating voltage 6132 higher than the peak voltage of the AC mains. 6133
TOV is caused by a fault in the power distribution system and occurs rarely. Moreover, the 6134 chance of an SPD fault occurring simultaneously with a TOV is negligible for determination of 6135 SPC specification. Therefore, it is required that the surge suppressor shall not operate during 6136 the TOV under normal operating conditions. 6137
The surge suppressor with any single fault condition shall not operate by a voltage fluctuation 6138 of the mains, since the voltage fluctuation occurs during normal operation of the power 6139 distribution system. 6140
A.3 Considerations on a surge suppresser used for ID1 external circuit in 6141 class II equipment 6142
Details of the three conditions for specification of a surge suppressor bridging an external 6143 circuit ID1 and the mains are described below. 6144
A.3.1 Lightning surges flow from mains circuit to external circuit 6145
It is not necessary to prevent the flow of lightning surges from the mains to an external circuit 6146 ID1 since it does not affect the safety of the external circuit. 6147
Surge voltages often appear at telecommunication lines classified as ID 1 in Table 13 6148 electromagnetically induce or conductively flow from lightning stroke near by the line. The 6149 lightning surge voltage can be higher than 10 kV at telecommunication lines; details are 6150 described in Chapter 10 of CCITT Handbook (CCITT Handbook, “The Protection of 6151 Telecommunication Lines and Equipment Against Lightning Discharges - Chapters 9 and 10”). 6152
Even if a surge suppresser bridging the mains and an external circuit ID1 operates by a surge, 6153 it does not change the safety condition of the external circuit since the AC mains current does 6154 not flow and the surge from the mains to the external circuit is reduced by a varistor in the 6155 surge suppressor. 6156
The details of operation and surge flow in an example of surge suppressor is described below. 6157
The surge voltage through a MOV decreases as much as the voltage between the terminals of 6158 the MOV (VMOV) when the surge flows through the MOV. Therefore, even if the 2 500 V 6159 maximum surge appears on the power line, the surge voltage at the telecommunication port 6160 (Vtel) is expected to decrease by VMOV and becomes less than 1 500 V, provided a typical value 6161 MOV is incorporated in the circuit (see Figure A.4 and Figure A.5). The MOV stops the current 6162 when the mains voltage is lower than VMOV, so an AC current does not flow through the MOV 6163 even if it operates by a surge voltage. Therefore, it does not cause an ES1/ES2 external circuit 6164 to become ES3. This means any degradations of safety are not caused by the surge flow 6165 through the surge suppressor. 6166
– 181 – 108/757/DC
6167
Figure A.5 – An example of surge voltage drop by a MOV and two GDTs (measured in 6168 laboratory) 6169
A.3.2 TOV on power distribution system failure 6170
A.3.2.1 General 6171
When a fault occurs at a power distribution transformer at a power substation, a TOV appears 6172 on the mains. The surge suppressor under normal operating conditions shall not operate 6173 under the TOV condition. However, it is not reasonable to consider the condition that other 6174 faults occur simultaneously in the surge suppressor and the power distribution system since the 6175 TOV occurs very rarely. If the operation voltage of the surge suppressor is determined not to 6176 operate under the condition that faults are occurring in both the power system and the surge 6177 suppressor, the operation voltage of the surge suppressor has to be too high to protect 6178 equipment efficiently. 6179
A.3.2.2 TOV in countries 6180
The stress for equipment in low voltage installations conditions are described as TOV in 6181 IEC 60364-4-44. The maximum voltage of the TOV is shown in Table A.1. 6182
In TN system, TOV is the nominal mains voltage U0, if the surge suppresser is bridging the 6183 mains and PEN, but it shall be noted that TOV reaches U0 + 1 200 V between the mains and 6184 an external circuit on the worst case if PEN is not connected to the equipment. 6185
Table A.1 – Permissible power-frequency stress voltage (except for US and Japan) 6186
Duration of the earth fault in the high-voltage system
t (second)
Permissible power-frequency stress voltage on equipment in low-voltage installations
U (Vrms)
> 5 U0 + 250
≤ 5 U0 + 1200
6187
U0 in TN and TT system: nominal AC r.m.s. line voltage to earth 6188
in IT-systems: nominal AC voltage between line conductor and neutral conductor or mid point 6189 conductor, as appropriate 6190
In systems without a neutral conductor, U0 shall be the line to line voltage. 6191
Additional information of TOV parameters in USA and Japan are provided in IEC 61643-12:2020. 6192 The TOV values are provided in Table A.2 and Table A.3. 6193
– 182 – 108/757/DC
Table A.2 – TOV parameters for US systems quoted from IEC 61643-12:2020 6194
Clause # and Category of Table 2 of IEEE 1159-2009
Typical max duration
(s)
Typical max rms-voltage (V)
Typical peak voltage (V)
SPD TOV
Withstand
-+ 5 %
2.0 Short duration variation -
2.1 Instantaneous- 2.1.2 Swell
0,5
1,8 x U0
(207 Vrms)
2,55 x U0
(294 Vpeak)
1,89
2.0 Short duration variation-
2.2 Momentary-2.2.2 Swell
3,0
1,4 x U0
(161 Vrms)
1,98 x U0
(223 Vpeak)
1,47
2.0 Short duration variation-
2.3 Tempory-2.3.3 Swell
60,0
1,2 x U0
(138 Vrms)
1,70 x U0
(196 Vpeak)
1,26
Table A.3 – TOV test parameters for Japanese systems quoted from IEC 61643-12:2020 6195
Application TOV test parameters
SPDs connected to For tT = 120 min
(LV-system faults in distribution system and loss of neutral)
For tT = 1 s (HV-system faults)
Withstand or safe end of life acceptable
Withstand or safe end of life acceptable
TOV test values UT
V
Prospective short-circuit
current A
TOV test values UT
V
Prospective short-circuit
current A
Nominal AC system voltage 100V
Connected L-PE 330 20 710 30 Connected L-N 330 20
Connected N-PE 600 30
Connected L-L
Nominal AC system voltage 200V
Connected L-PE 330 20 820 30
Connected L-N 330 20
Connected N-PE 600 30
Connected L-L
Nominal AC system voltage 400V
Connected L-PE 440 20 855 300
Connected L-N 440 20
Connected N-PE 600 300
Connected L-L
NOTE These values are required by ministerial ordinance of technical standards for electrical facilities.
6196
A.3.2.3 TOV for mains nominal voltages 6197
A.3.2.3.1 Countries conforming to IEC 60364-4-44 other than US and Japan 6198
For setting the requirement for a surge suppressor, the TOV for a duration shorter than or equal 6199 to 5 s shall be considered since it is higher than for longer duration. Table A.4 shows the 6200 calculated peak voltages in countries conforming IEC 60364-4-44. 6201
– 183 – 108/757/DC 6202
Table A.4 – Peak voltage of TOV in countries conforming IEC 60364-4-44 6203
U0 U0 + 1 200 (U0 + 1 200) x 1,414
(Round up)
100 1300 1839
115 1315 1860
120 1320 1867
200 1400 1980
220 1420 2008
230 1430 2023
240 1440 2037
400 1600 2263
6204
A.3.2.3.2 Peak voltage of TOV in US and Japan 6205
For setting the requirement for a surge suppressor, the TOV for a duration shorter than or equal 6206 to 0,5 s in Table A.2 is considered. Table A.5 shows the calculated peak voltage in the US. 6207
Table A.5 – Peak voltage of TOV in US 6208
U0 TOV (r.m.s)
U0 x 1,8
Peak voltage of TOV
U01.8 x 1,414
115 207 293
230 414 586
400 720 1019
6209
For setting the requirement for surge suppresser, the TOV for duration of shorter or equal to 1 6210 second in Table A.3 is considered. Table A.6 show calculated peak voltage in Japan. 6211
6212
Table A.6 – Peak voltage of TOV in Japan 6213
U0 TOV
(RMS)
Peak voltage of TOV
TOV (RMS) x 1,414
100 710 1004
200 820 1160
400 855 1209
6214
A.3.2.4 Requirement for a surge suppressor relating to TOV 6215
A surge suppressor bridging the mains and an external circuit shall not operate when a DC 6216 voltage of UTOV2 is applied between the primary circuit and an external circuit within the 6217 equipment. 6218
For power systems complying with the IEC 60364 series (countries other than USA and 6219 Japan), UTOV2 is derived as follows from the peak voltages in Table A.4 6220
– for a nominal voltage of the mains lower than or equal to 120 V, UTov2 = 2 000 V 6221
– for a nominal voltage of the mains lower than or equal to 230 V, UTov2 = 2 500 V 6222
– 184 – 108/757/DC For power systems in USA and Japan, UTOV2 is derived as follows from the peak voltages in 6223 Table A.5 and Table A.6. 6224
- for a nominal voltage of the mains lower than or equal to 400 V, UTov2 = 1 500 V 6225
A.3.3 Voltage fluctuation 6226
A.3.3.1 Voltage fluctuation value 6227
The voltage fluctuation of the mains voltage is in many countries less than 10 % of the nominal 6228 mains voltage. For safety reasons it is assumed that maximum fluctuation of the mains voltage 6229 is set to 120 % of the nominal mains voltage for the calculation of the operation voltage of 6230 surge suppressor under single fault condition of the surge suppresser. 6231
The value 120 % of the nominal mains voltage is the same as the test voltage for ICX in G.16 6232 of IEC 62368-1. 6233
The peak voltage of the AC mains voltage at the maximum of the fluctuation Upeak2 is calculated 6234 as Upeak2 = U0 x 1,2 x 1,414. 6235
The calculated values for major mains voltages in the world are listed in Table A.7. 6236
Table A.7 – The value of Upeak2 for major mains voltages 6237
U0 U0 x 1,2 Upea2 = U0 x 1,2 x 1,414
(Round up)
100 120 170
115 138 196
120 144 204
200 240 340
220 264 374
230 276 391
240 288 408
400 480 679
6238
A.3.3.2 Requirement on surge suppressor when it has a single fault 6239
A surge suppressor usually consists of combination of SPCs including MOVs and GDTs. The 6240 surge suppressor bridging between the mains and an external circuit shall not operate when 6241 a DC voltage of Upeak2 as shown in Table A.7 is applied between the mains and an external 6242 circuit, even if anyone of the SPCs constituting the surge suppresser is short-circuited. 6243
The operation voltage of the SPC shall be specified not to operate at Upeak2, considering the 6244 variations in SPC production (ΔUsp) and change of the rated operating voltage due to the SPC 6245 ageing over the expected lie of the equipment (ΔUsa). The lower limit of the operation voltage 6246 is Uop = Upeak+∆Usp+∆Usa. (see 5.4.11.2 of IEC 62368-1:2022). 6247
A.3.4 A note on leakage of hazardous voltage to the other external ports 6248
Figure A.6 shows an example of ports configured to telecommunication equipment that do not 6249 have an earthing connection. The TOV will not go to the external circuits A, B and C if any 6250 part of the surge suppresser is not connected to the circuit in the equipment. This means the 6251 safety condition does not differ from the equipment that does not have bridging by surge 6252 suppresser. The surge voltage at the external circuit does not remarkably change by bridging. 6253
The ES1 or ES2 circuits driving and receiving external ports is separated from the 6254 telecommunication cable (ID 1 of Table 13) for safeguards against transient voltages from 6255 external circuits. Impulse test of 1.5 kV 10/700 or steady state test of 1.0 kV is required for this 6256 purpose. 6257
– 185 – 108/757/DC Hazardous voltage is stopped by the isolation described above, and safety is kept at the 6258 external ports such as A, B and C. 6259
By the reasons above, the bridging of the mains and the telecommunication port does not cause 6260 an increase of hazardous voltage leak to the other ports. 6261
6262
Figure A.6 – An example of ports of telecommunication equipment 6263
A.4 Information about follow current (or follow-on current) 6264
A.4.1 General 6265
The information was taken from “MITSUBISHI Materials home page” 6266
A.4.2 What is follow-on-current? 6267
Follow-on-current is an electric current that will continue to flow. In this case it is a phenomenon 6268 where the current in a discharge tube continues to flow. 6269
Normally surge absorbers are in a state of high impedance. When a surge enters the absorber 6270 it will drop to a low impedance, allowing the surge to bypass the electronic circuit it is protecting. 6271 After the surge has passed, the absorber should return to a high impedance. 6272
However, when the absorber is in a low impedance state and there is sufficient voltage on the 6273 line to keep the current flowing when the surge ends, and the absorber remains in a discharge 6274 state and does not return to a high impedance state, the current will continue to flow. This is a 6275 phenomenon known as follow-on-current. 6276
Surge absorbers that display this follow-on-current are of the discharge type and semiconductor 6277 switching type. A characteristic of these absorbers is that during surge absorption (bypass) the 6278 operating voltage (remaining voltage) is lower than the starting voltage. 6279
– 186 – 108/757/DC The advantage of these surge absorbers is that during suppression the voltage is held very low, 6280 so it reduces stress on the equipment. However, a problem arises when the line current of the 6281 equipment is high enough to continue to drive the absorber even when the voltage is low. 6282
Follow-on current mechanisms are explained further in the following sub-clauses. 6283
A.4.3 What are the V-I properties of discharge tubes? 6284
The micro-gap type surge absorber is a type of a discharge tube. The discharge in the tube 6285 changes from pre-discharge to glow discharge and then to arc discharge as shown in Figure A.7 6286 in this document. 6287
Figure A.7 in this document shows the V-I characteristics between voltage and current for the 6288 discharge tube. When the tube is discharging, electric current flows and moves to a glow 6289 discharge and then to an arc discharge as the discharge voltage decreases. On the other hand, 6290 when the discharge decreases, the voltage increases as it moves from an arc discharge to a 6291 glow discharge. 6292
6293
Figure A.7 – V-I properties of gas discharge tubes 6294
Pre-glow discharge 6295
The voltage to maintain the discharge is approximately equal to the DC breakdown voltage. A 6296 faint light can be seen at this point. 6297
Glow discharge 6298
The constant voltage rate remains as the current changes. The voltage to maintain the 6299 discharge depends on the electrode material and the gas in the tube. The discharge light covers 6300 a portion of the electrodes. 6301
Arc discharge 6302
At this discharge, a large current flows through the part and it puts out a bright light. The 6303 maintaining voltage at this point (voltage between the discharge tube terminals) is in the 10’s 6304 of volts range. 6305
– 187 – 108/757/DC A.4.4 What is holdover? 6306
When a discharge tube is used on a circuit that has a DC voltage component, a phenomenon 6307 occurs, called holdover, where the discharge in the tube continues to be driven by the current 6308 from the power supply even after the surge voltage has subsided (see Figure A.8 in this 6309 document). 6310
When a holdover occurs, for example, in the drive circuit of a CRT, the screen darkens and 6311 discharge in the absorber continues, which can lead to the glass tube melting, smoking or 6312 burning. 6313
(a) No holdover occurring (b) Holdover occurring
Figure A.8 – Holdover 6314
Holdover can occur when the current is supplied to the discharge tube due to varying conditions 6315 of output voltage and output resistance of the DC power supply. What are the conditions that 6316 allow current to continue to flow to the discharge tube? 6317
The relation between the power supply voltage (V0), serial resistance (R), discharge current (I) 6318 and the terminal voltage (v) are shown in the linear relation below: 6319
v = V0 – I x R 6320
If the voltage V0 is fixed, the slope of the power supply output characteristic line increases or 6321 decreases according to the resistance and may or may not intersect with the V-I characteristics 6322 of the discharge tube. 6323
The characteristic linear line of a power supply shows the relation between the output voltage 6324 and current of the power supply. Likewise, the V-I curve of a discharge tube shows the relation 6325 between the voltage and the current. 6326
When static surge electricity is applied to the discharge tube, the shape of the curve shows that 6327 the surge is being absorbed during arc discharge. 6328
As the surge ends, the discharge goes from arc discharge to glow discharge and then to a state 6329 just prior to glow discharge. At this time the relationship between the discharge tubes V-I curve 6330 and the power supply’s output characteristics are very important. 6331
(a) As shown in At low resistance 6332
, with a high resistance in the power supply, the output characteristic line (pink) and the 6333 discharge tubes V-I characteristic curve (black) never intersect. Therefore, current will not flow 6334 from the power supply and follow-on-current will not occur. 6335
– 188 – 108/757/DC However, when the output characteristic line of the power supply (red) intersects with the V-I 6336 curve of the discharge tube (black), it is possible for the current from the power supply to flow 6337 into the discharge tube. When the surge ends, the current should decrease from arc discharge 6338 to the pre-glow state, but instead the current will continue to flow where it intersects in the glow 6339 or arc discharge region. This condition where the power supply continues to allow current into 6340 the discharge tube is called holdover. 6341
Figure A.9 in this document shows how the power supply continues to supply current to the 6342 discharge tube when its characteristic line intersects the discharge tubes V-I line in the glow or 6343 arc discharge sections. 6344
Figure A.9 – Relation of the V-I characteristic of a gas discharge tube and the output 6345 characteristic of the power supply 6346
To prevent holdover from occurring, it is important to keep the V-I characteristic line of the 6347 power supply from intersecting with the V-I curve of the discharge tube. 6348
A.4.5 Follow-on-current from AC sources 6349
In Figure A.11, the only difference is that the power supply voltage (V0) changes with time. 6350
As shown in A.4.4, when the power supply voltage is shown as V0(t), the output power 6351 characteristics are displayed as follows: 6352
v = V0(t) – R x I 6353
where 6354
v is the the voltage at the power out terminal 6355
I is the current of the circuit 6356
V0(t) will vary with time, so when displaying the above equation on a graph, it will appear 6357 as in Figure A.10 in this document. Then when V0 (t) is shown as: 6358
V0(t) = V0 sin wt 6359
When the power supply voltage becomes 0 (zero cross), there is a short time when the voltage 6360 range and time range of the power supply output and discharge tube V-I curve do not intersect. 6361
For an AC power supply, because there is always a zero crossing of the supply’s voltage, it is 6362 easier to stop the discharge than in the case of a DC power supply. In the vicinity of the zero 6363 crossing, it is impossible to maintain the discharge since the current to the discharge is cut off. 6364 The discharge is then halted by ionized gas molecules returning to their normal state. 6365
– 189 – 108/757/DC Because the terminal voltage does not exceed the direct current break down voltage, if the 6366 discharge is halted it will not be able to start again. 6367
However, if the gas molecules remain ionized during this period and voltage is again applied to 6368 both terminals of the discharge tube (enters the cycle of opposite voltage), this newly applied 6369 voltage will not allow the discharge to end and it will continue in the discharge mode. This is 6370 follow-on-current for alternating current. 6371
When this type of follow-on-current occurs, the tube stays in a discharge mode and the glass 6372 of the tube will begin to smoke, melt and possibly ignite. 6373
6374
(b) At high resistance 6375
6376
(c) At low resistance 6377
Figure A.10 – Characteristics 6378
It is important to utilize a resistance in series that is sufficiently large enough to prevent follow-6379 on-current from occurring according to the conditions of the alternating current. 6380
– 190 – 108/757/DC
Picture 1: with 0 Ω (follow-on current occuring)
Picture 2: with 0,5 Ω (follow-on current is stopped within half a wave)
Figure A.11 – Follow on current pictures 6381
With 1 Ω and 3 Ω resistance, results are the same as those in picture 2, follow-on-current is 6382 interrupted and discharge is stopped (see Figure A.11 in this document). 6383
For AC power sources, the resistance value that is connected in series with the discharge tube 6384 is small in comparison to DC sources. 6385
If the series resistance is 0,5 Ω or greater it should be sufficient, however for safety a value of 6386 3 Ω (for 100 V) or greater is recommended. 6387
In addition, there is a method to use a varistor in series that acts as a resistor. In this case the 6388 varistor should have an operating voltage greater than the AC voltage and be placed in series 6389 with the discharge tube. Unlike the resistor, discharge will be stopped without follow-on-current 6390 occurring during the first half of the wave. 6391
Recommended varistor values are: 6392
– a varistor voltage of 220 V minimum for 100 VAC; 6393
– a varistor voltage of 470 V minimum for 200 VAC. 6394
6395
– 191 – 108/757/DC
Annex B 6396
(informative) 6397
6398
Background information related to measurement of discharges – 6399
Determining the R-C discharge time constant for X- and Y-capacitors 6400
B.1 General 6401
Since the introduction of 2.1.1.7, “Discharge of capacitors in equipment,” in IEC 60950-1:2013, 6402 questions continually arise as to how to measure the R-C discharge time constant. The objective 6403 of this article is to describe how to measure and determine the discharge time constant. 6404
B.2 EMC filters 6405
EMC filters in equipment are circuits comprised of inductors and capacitors arranged so as to 6406 limit the emission of RF energy from the equipment into the mains supply line. In EMC filters, 6407 capacitors connected between the supply conductors (for example, between L1 and L2) of the 6408 mains are designated as X capacitors. Capacitors connected between a supply conductor and 6409 the PE (protective earthing or grounding) conductor are designated as Y capacitors (Safety 6410 requirements for X and Y capacitors are specified in IEC 60384-14 and similar national 6411 standards). The circuit of a typical EMC filter is shown in Figure B.1. CX is the X capacitor, and 6412
CY are the Y capacitors. 6413
6414
Figure B.1 – Typical EMC filter schematic 6415
B.3 The safety issue and solution 6416
When an EMC filter is disconnected from the mains supply line, both the X (Cx) and the Y (CYa 6417
and CYb) capacitors remain charged to the value of the mains supply voltage at the instant of 6418
disconnection. 6419
Due to the nature of sinusoidal waveforms, more than 66 % of the time (30° to 150° and 210° 6420 to 330° of each cycle) the voltage is more than 50 % of the peak voltage. For 230 V mains (325 6421 Vpeak), the voltage is more than 162 V for more than 66 % of the time of each cycle. So, the 6422
– 192 – 108/757/DC probability of the voltage exceeding 162 V at the time of disconnection is 0,66. This probability 6423 represents a good chance that the charge on the X and Y capacitors will exceed 162 V. 6424
If a hand or other body part should touch both pins (L1 and L2) of the mains supply plug at the 6425 same time, the capacitors will discharge through that body part. If the total capacitance exceeds 6426 about 0,1 µF, the discharge will be quite painful. 6427
To safeguard against such a painful experience, safety documents require that the capacitors 6428 be discharged to a non-painful voltage in a short period of time. The short period of time is 6429 taken as the time from the disconnection from the mains to the time when contact with both 6430 pins is likely. Usually, this time is in the range of 1 s to 10 s, depending on the documents and 6431 the type of attachment plug cap installed. 6432
B.4 The requirement 6433
The time constant is measured with an oscilloscope. The time constant and its parameters are 6434 defined elsewhere. 6435
The significant parameters specified in the requirement are the capacitance exceeding 0,1 µF 6436 and the time constant of 1 s or less (for pluggable equipment type A) or 10 s or less (for 6437 pluggable equipment type B). These values bound the measurement. This attachment 6438 addresses pluggable equipment type A and the 1 s time constant requirement. The 6439 attachment applies to pluggable equipment type B and the time constant is changed to 10 s. 6440
Pluggable equipment type A is intended for connection to a mains supply via a non-industrial 6441 plug and socket-outlet. Pluggable equipment type B is intended for connection to a mains 6442 supply via an industrial plug and socket-outlet. 6443
The document presumes that measurements made with an instrument having an input 6444 resistance of 95 MΩ to 105 MΩ and up to 25 pF in parallel with the impedance and capacitance 6445 of the equipment under test (EUT) will have negligible effect on the measured time constant. 6446 The effect of probe parameters on the determination of the time constant is discussed 6447 elsewhere in this document. 6448
The requirement specifies a time constant rather than a discharge down to a specified voltage 6449 within a specified time interval. If the document required a discharge to a specific voltage, then 6450 the start of the measurement would need to be at the peak of the voltage. This would mean that 6451 the switch (see Figure B.5) would need to be opened almost exactly at the peak of the voltage 6452 waveform. This would require special switching equipment. The time constant is specified 6453 because it can be measured from any point on the waveform (except zero), see Figure B.4 b). 6454
B.5 100 MΩ probes 6455
Table B.1 in this document is a list of readily available oscilloscope probes with 100 MΩ input 6456 resistance and their rated input capacitances (the list is not exhaustive). Also included is a 6457 400 MΩ input resistance probe and a 50 MΩ input resistance probe. 6458
– 193 – 108/757/DC
Table B.1 – 100 MΩ oscilloscope probes 6459
Manufacturer Input resistance
MΩ
Input capacitance
pF
A 100 1
B 100 6,5
C 100 3
D 400 10 – 13
E 100 2,5
F 50 5,5
6460
Note that the input capacitances of the 100 MΩ probe input capacitances are very much less 6461 than the maximum capacitance of 25 pF. This attachment will discuss the effect of the probe 6462 capacitance and the maximum capacitance elsewhere. 6463
100 MΩ probes are meant for measuring high voltages, typically 15 kV and more. These probes 6464 are quite large and are awkward to connect to the pins of a power plug. 6465
6466
Figure B.2 – 100 MΩ oscilloscope probes
General purpose oscilloscope probes have 10 MΩ input resistance and 10 pF to 15 pF input 6467 capacitance. General-purpose probes are easier to connect to the pins of the power plug. This 6468 attachment shows that a 10 MΩ, 15 pF probe can be used in place of a 100 MΩ probe. 6469
B.6 The R-C time constant and its parameters 6470
Capacitor charge or discharge time can be expressed by the R-C time constant parameter. One 6471 time constant is the time duration for the voltage on the capacitor to change 63 %. In five time 6472 constants, the capacitor is discharged to almost zero. 6473
– 194 – 108/757/DC
Table B.2 – Capacitor discharge 6474
Time constant Percent capacitor voltage (or charge)
Capacitor voltage
(230 Vrms, 331 Vpeak)
0 100 325
1 37 120
2 14 45
3 5 16
4 2 6
5 0,7 2
6475
The values in Table B.2 in this document are given by: 6476
)(
0RCt
t eVV−
= 6477
where: 6478
tV is the voltage at time t 6479
0V is the voltage at time 0 6480
R is the resistance, in Ω 6481
C is the capacitance, in F (Farads) 6482
t is the time, in s 6483
6484
The time constant is given by the formula: 6485
EUTEUTEUT CRT ×= 6486
where: 6487
EUTT is the time, in seconds, for the voltage to change by 63 % 6488
EUTR is the EUT resistance, in Ω 6489
EUTC is the EUT capacitance, in F (Farads) 6490
In the equipment under test (EUT), the EUT capacitance, CEUT, in the line filter (Figure B.1) 6491
includes both the X-capacitor and the Y-capacitors. 6492
The two Y-capacitors, CYa and CYb, are in series. The resultant value of two capacitors in series, 6493
CY, is: 6494
YbYa
YbYaY CC
CCC
+×
= 6495
Assuming the two Y-capacitors have the same value, their L1-L2 value is one-half of the value 6496 of one of the capacitors. 6497
– 195 – 108/757/DC The X-capacitor is in parallel with the two Y-capacitors. The EUT capacitance is: 6498
YXEUT CCC += 6499
The EUT resistance is the resistance, REUT, in the EUT that is used for discharging the 6500
capacitance. 6501
The time constant, TEUT, in s, is the product of the EUT capacitance in farads and the EUT 6502
resistance in Ω. More useful units are capacitance in µF and resistance in MΩ. 6503
Two parameters of the time constant formula are given by the requirement: EUT capacitance is 6504 0,1 µF or larger and the EUT time constant does not exceed 1 s. Solving the time constant 6505 formula for EUT resistance: 6506
EUTEUTEUT CTR = 6507
Substituting the values: 6508
1 / 0,1EUTR s Fµ= 6509
10 Ω= MREUT 6510
This means that the EUT resistance is no greater than 10 MΩ if the EUT capacitance is 0,1 µF 6511 or greater. The combinations of EUT resistance and EUT capacitance for EUT time constant of 6512 1 s are shown in Figure B.3 in this document. 6513
Figure B.3 – Combinations of EUT resistance and capacitance for 1 s time constant
– 196 – 108/757/DC
B.7 Time constant measurement. 6514
The objective is to measure and determine the EUT time constant. 6515
Measurement of the time constant is done with an oscilloscope connected to the mains input 6516 terminals of the equipment under test (EUT). Mains is applied to the EUT, the EUT is turned 6517 off, and then the mains is disconnected from the EUT. The EUT is turned off because the load 6518 circuits of the EUT may serve to discharge the EUT capacitance. The resulting oscilloscope 6519 waveform, the AC mains voltage followed by the discharge of the total capacitance, is shown 6520 in Figure B.4 in this document. 6521
– 197 – 108/757/DC
a) 240 V mains followed by capacitor discharge V = 50 V/div, H = 1 s/div
6522
b) 240 V mains followed by capacitor discharge V = 50 V/div, H = 0,2 s/div
Figure B.4 – 240 V mains followed by capacitor discharge 6523
The time constant is the time duration measured from the instant of disconnection to a point 6524 that is 37 % of the voltage at the instant of disconnection. 6525
The problem is that the process of measurement affects the measured time constant. This is 6526 because the oscilloscope probe has a finite resistance and capacitance, see Figure B.5 in this 6527 document. 6528
– 198 – 108/757/DC
Figure B.5 – Time constant measurement schematic 6529
The probe resistance, Rprobe, is in parallel to the EUT resistance, REUT. And, the probe 6530
capacitance, Cprobe, is in parallel with the EUT capacitance, CEUT. 6531
The measured time constant, Tmeasured, is a function of the Thevenin equivalent circuit 6532
comprised of Rtotal and Ctotal. The measured time constant is given by: 6533
totaltotalmeasured CRT ×= 6534
where: 6535
measuredT is the measured time for the voltage to change by 63 % 6536
totalR is the total resistance, both the probe and the EUT 6537
totalC is the total capacitance, both the probe and the EUT 6538
Rtotal is: 6539
EUTprobe
EUTprobetotal RR
RRR
+
×= 6540
Ctotal is: 6541
Combining terms, the measured time constant is: 6542
)()( EUTprobeEUTprobe
EUTprobemeasured CC
RRRR
T +×+
×= 6543
– 199 – 108/757/DC In this formula, Tmeasured, Rprobe, and Cprobe are known. Tmeasured is measured with a given 6544
probe. Rprobe and Cprobe are determined from the probe specifications (see examples in 6545
Table B.1 in this document). Elsewhere, we shall see that Cprobe is very small and can be 6546
ignored. 6547
EUTtotal CC = 6548
The measured time constant can now be expressed as: 6549
totalEUTprobe
EUTprobemeasured C
RRRR
T ×+
×= )( 6550
B.8 Effect of probe resistance 6551
As has been shown, the EUT discharge resistance, REUT, is 10 MΩ or less in order to achieve 6552
a 1 s time constant with a 0,1 µF capacitor or larger. 6553
Rtotal is comprised of both the EUT discharge resistance REUT, and the probe resistance, Rprobe. 6554
If REUT is 10 MΩ and CEUT is 0,1 µF, then we know that TEUT is 1 s. If we measure the time 6555
constant with a 100 MΩ probe, the parallel combination of REUT and Rprobe is about 9,1 MΩ and 6556
the measured time constant, Tmeasured, will be: 6557
totaltotalmeasured CRT ×= 6558
FMTmeasured µ1,01,9 ×Ω= 6559
sTmeasured 91,0= 6560
So, for a CEUT of 0,1 µF capacitance and a REUT of 10 MΩ, a measured time constant (using a 6561
100 MΩ probe), Tmeasured, of 0,91 s would indicate a EUT time constant, TEUT, of 1 s. 6562
If we substitute a 10 MΩ probe for the same measurement, then Rtotal, the parallel combination 6563
of REUT (10 MΩ) and Rprobe (10 MΩ), is 5 MΩ. The measured time constant, Tmeasured, will be: 6564
totaltotalmeasured CRT ×= 6565
FMTmeasured µ1,05 ×Ω= 6566
sTmeasured 5,0= 6567
So, for a CEUT of 0,1 µF capacitance and a REUT of 10 MΩ, the measured time constant (using 6568
a 10 MΩ probe), Tmeasured, is 0,5 s and would indicate a EUT time constant, TEUT, of 1 s. 6569
– 200 – 108/757/DC
B.9 Effect of probe capacitance 6570
According to the document, CEUT is 0,1 µF or more. Also, according to the document, Cprobe is 6571
25 pF or less. Assuming the worst case for Cprobe, the total capacitance is: 6572
EUTprobetotal CCC += 6573
uFuFCtotal 1,0000025,0 += 6574
uFCtotal 100025,0= 6575
The worst-case probe capacitance is extremely small (0,025 %) compared to the smallest CEUT 6576
capacitance (0,1 µF) and can be ignored. We can say that: 6577
EUTtotal CC = 6578
B.10 Determining the time constant 6579
According to the document, TEUT may not exceed 1 s. 6580
1=EUTT 6581
EUTEUT CR ×=1 6582
where: 6583
EUTR is 10 MΩ or less 6584
EUTC is 0,1 µF or more 6585
The problem is to determine the values for REUT and CEUT. Once these values are known, the 6586
equipment time constant, TEUT, can be determined by calculation. 6587
As shown in Figure B.1 in this document, REUT can be measured directly with an ohmmeter 6588
applied to the mains input terminals, for example, between L1 and L2. Care is taken that the 6589 capacitances are fully discharged when the resistance measurement is made. Any residual 6590 charge will affect the ohmmeter and its reading. Of course, if the circuit is provided with a 6591 discharge resistor, then the capacitances will be fully discharged. If the circuit does not have a 6592 discharge resistor, then the ohmmeter will provide the discharge path, and the reading will 6593 continuously increase. 6594
CEUT can also be measured directly with a capacitance meter. Depending on the particular 6595
capacitance meter, REUT may prevent accurate measurement of CEUT. For the purposes of this 6596
paper, we assume that the capacitance meter cannot measure the CEUT. In this case, we 6597
measure the time constant and compensate for the probe resistance. 6598
So, the time constant is measured, and the probe resistance is accounted for. 6599
Since probe resistance is more or less standardized, we can calculate curves for 100 MΩ and 6600 10 MΩ probes for all maximum values of REUT and CEUT. The maximum values for combinations 6601
– 201 – 108/757/DC of REUT, CEUT (Ctotal), Rprobe, Rtotal and Tmeasured are given in Table B.3 in this document. 6602
(Rprobe and Rtotal values are rounded to 2 significant digits.) 6603
Table B.3 – Maximum Tmeasured values for combinations of REUT 6604
and CEUT for TEUT of 1 s 6605
TEUT
s
CEUT (Ctotal)
µF
REUT
MΩ
Rprobe
MΩ
Rtotal
MΩ
Tmeasured
s
1 0,1 10 100 9,1 0,91
1 0,2 5 100 4,8 0,95
1 0,3 3,3 100 3,2 0,97
1 0,4 2,5 100 2,4 0,97
1 0,5 2 100 2,0 0,98
1 0,6 1,7 100 1,6 0,98
1 0,7 1,4 100 1,4 0,99
1 0,8 1,25 100 1,2 0,99
1 0,9 1,1 100 1,1 0,99
1 1,0 1 100 1,0 0,99
1 0,1 10 10 5,0 0,50
1 0,2 5 10 3,3 0,67
1 0,3 3,3 10 2,5 0,75
1 0,4 2,5 10 2,0 0,80
1 0,5 2 10 1,7 0,83
1 0,6 1,7 10 1,4 0,86
1 0,7 1,4 10 1,25 0,88
1 0,8 1,25 10 1,1 0,89
1 0,9 1,1 10 1,0 0,90
1 1,0 1 10 0,91 0,91
6606
For each value of REUT and Rprobe we can calculate the worst-case measured time constants, 6607
Tmeasured for a TEUT of 1 s. These are shown in Figure B.6 in this document. 6608
The process is: 6609
– With the unit disconnected from the mains and the power switch “off,” measure the 6610 resistance between the poles of the EUT. Repeat with the power switch “on” as the filter 6611 may be on the load side of the power switch. Select the higher value as REUT. 6612
– Connect the oscilloscope probe between L1 and L2 as shown in Figure B.5 in this document. 6613 For safety during this test, use a 1:1 isolating transformer between the mains and the EUT. 6614 Set the scope sweep speed to 0,2 ms per division (2 s full screen). 6615
– When the display is about 1 or 2 divisions from the start, turn the test switch off, and measure 6616 the time constant as shown in Figure B.4 in this document. This step may need to be 6617 repeated several times to get a suitable waveform on the oscilloscope. This step should be 6618 performed twice, once with the EUT power switch “off” and once with the EUT power switch 6619 “on.” Select the maximum value. This value is Tmeasured. 6620
– Plot REUT and Tmeasured on the chart, Figure B.6 in this document. 6621
– 202 – 108/757/DC If the point is below the curve of the probe that is used to measure the time constant, then the 6622 EUT time constant, TEUT, is less than 1 s. 6623
6624
Figure B.6 – Worst-case measured time constant values for 100 MΩ and 10 MΩ probes 6625
B.11 Conclusion 6626
Measurement of the time constant can be made with any probe, not just a 100 MΩ probe. Ideally, 6627 the probe input resistance should be at least equal to the worst-case EUT discharge resistance 6628 (10 MΩ for pluggable equipment type A) or higher. The effect of the probe input resistance is 6629 given by the equation for Rtotal. 100 MΩ probes, while approaching ideal in terms of the effect 6630
on the measured time constant, are bulky and expensive and not necessary. 6631
The document is a bit misleading by ignoring a 9 % error when a 100 MΩ probe is used to 6632 measure the time constant associated with a 10 MΩ discharge resistor (see Figure B.5 in this 6633 document). 6634
6635
– 203 – 108/757/DC
Annex C 6636
(informative) 6637
6638
Background information related to resistance to candle flame ignition 6639
In line with SMB decision 135/20, endorsing the ACOS/ACEA JTF recommendations, the former 6640 Clause 11 was added to the document up to CDV stage. However, the CDV was rejected and 6641 several national committees indicated that they wanted to have the requirements removed from 6642 the document. At the same time, several countries indicated that they wanted the requirements 6643 to stay, while others commented that they should be limited to CRT televisions only. 6644
IEC TC 108 decided to publish the requirements as a separate document so that the different 6645 issues can be given appropriate consideration. 6646
6647
– 204 – 108/757/DC
Annex D 6648
(informative) 6649
6650
Surge suppressers used between mains and an external circuit ID1 as 6651
specified in Table 13 6652
In countries where a surge suppresser with a group of surge protective components 6653 (SPCs) is used between mains and an external circuit classified as ID1 in Table 13 in 6654 class II equipment without earthing; the following need to be taken into consideration. 6655
The separation between ES1 or ES2 circuits and the external circuit provided in the 6656 equipment shall withstand either the impulse test of 1,5 kV 10/700 or the steady state 6657 test of 1,0 kV in accordance with 5.4.10. 6658
An example of a circuit configuration of a surge suppressor in this condition is shown 6659 in Figure D.1. 6660
6661
Figure D.1 – Example of circuit configuration of a surge suppresser 6662
The blunt probe of Figure V.3 is used to check the accessibility of the circuit in which 6663 the SPCs are connected. 6664
A surge suppressor with a group of SPCs consisting of one or more varistors and one 6665 or more GDTs connected in series; shall comply with the following: 6666
– The surge suppressor does not operate when UTOV2 is applied between mains and 6667 the external circuit in the equipment, where UTOV2 is defined as a peak voltage 6668 simulating TOV (temporary overvoltage) condition that is determined depending on 6669 the nature of the AC voltage supply system in the country. 6670
– The surge suppressor does not operate when the peak voltage of the AC mains 6671 voltage at maximum of the fluctuation Upeak2 is applied between the mains and the 6672 external circuit in the equipment, even if any of the SPCs that is part of the surge 6673 suppressor is short-circuited. 6674
– The rated operating voltage Uop of a SPC that is part of the surge suppressor is 6675 designed in order to avoid operation under the condition of UTOV2 and Upeak2. The 6676 rated operating voltage of the SPC is determined taking into consideration variations 6677 in production and ageing effects. 6678
6679
6680
– 205 – 108/757/DC
Bibliography 6681
IEC 60065:2014, Audio, video and similar electronic apparatus – Safety requirements 6682
IEC 60215, Safety requirements for radio transmitting equipment – General requirements and 6683 terminology 6684
IEC 60364-4-43, Low-voltage electrical installations – Part 4-43: Protection for safety – 6685 Protection against overcurrent 6686
IEC 60364-5-52, Low-voltage electrical installations – Part 5-52: Selection and erection of 6687 electrical equipment – Wiring systems 6688
IEC 60364-5-54, Low-voltage electrical installations – Part 5-54: Selection and erection of 6689 electrical equipment – Earthing arrangements and protective conductors 6690
IEC 60446, Identification by colours or numerals2 6691
IEC TS 60479-2, Effects of current on human beings and livestock – Part 2: Special aspects 6692
IEC 60664-2 (all parts), Insulation coordination for equipment within low-voltage systems – Part 6693 2: Application guide 6694
IEC 60664-4:2005, Insulation coordination for equipment within low-voltage systems – Part 4: 6695 Consideration of high-frequency voltage stress 6696
IEC 60695-2 (all parts), Fire hazard testing – Part 2: Glowing/hot-wire based test methods 6697
IEC 60695-2-13, Fire hazard testing – Part 2-13: Glowing/hot-wire based test methods – Glow-6698 wire ignition temperature (GWIT) test method for materials 6699
IEC 60695-11-2, Fire hazard testing – Part 11-2: Test flames – 1 kW nominal pre-mixed flame 6700 – Apparatus, confirmatory test arrangement and guidance 6701
IEC 60950-1:2005, Information technology equipment – Safety – Part 1: General requirements 6702 IEC 60950-1:2005/AMD1:2009 6703 IEC 60950-1:2005/AMD2:2013 6704
IEC 61010-1, Safety requirements for electrical equipment for measurement, control, and 6705 laboratory use – Part 1: General requirements 6706
IEC 61051-1, Varistors for use in electronic equipment – Part 1: Generic specification 6707
ISO/IEC Guide 51:1999, Safety aspects — Guidelines for their inclusion in standards 6708
ITU-T K.21:2008, Resistibility of telecommunication equipment installed in customer premises 6709 to overvoltages and overcurrents 6710
EN 41003:2008, Particular safety requirements for equipment to be connected to 6711 telecommunication networks and/or a cable distribution system 6712
EN 60065:2002, Audio, video and similar electronic apparatus – Safety requirements 6713
___________ 2 This publication was withdrawn.
– 206 – 108/757/DC NFPA 70, National Electrical Code 6714
NFPA 79:2002, Electrical Standard for Industrial Machinery 6715
UL 1667, UL Standard for Safety Tall Institutional Carts for Use with Audio-, Video-, and 6716 Television-Type Equipment 6717
UL 1995, UL Standard for Safety for Heating and Cooling Equipment 6718
UL 2178, Outline for Marking and Coding Equipment 6719
UL 60065, Audio, Video and Similar Electronic Apparatus – Safety Requirements 6720
UL/CSA 60950-1, Information Technology Equipment – Safety – Part 1: General Requirements 6721
CAN/CSA C22.1, Information Technology Equipment – Safety – Part 1: General Requirements 6722
CSA C22.1-09, Canadian Electrical Code – Part I: Safety Standard for Electrical Installations – 6723 Twenty-first Edition 6724
ASTM C1057, Standard Practice for Determination of Skin Contact Temperature from Heated 6725 Surfaces Using A Mathematical Model and Thermesthesiometer 6726
EC 98/37/EC Machinery Directive 6727
6728
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6730